Polyelectrolyte complexation is a rapidly growing field with applications in functional multilayer (PEM) and nanoparticle (PEC) generation, where PEM films are deposited using Layer-by-Layer technique initiated by Decher and PECs are prepared using mixing-centrifugation technique initiated by our group. Its advantages (e.g. easy preparation) result in various applications in aqueous solution, especially in pharmaceutical and biomedical fields. Therefore, the objectives in this study are to explore interesting applications of polyelectrolyte complexation in the field of low molecular chiral compound and high molecular protein binding. Due to the rapidly growing demands for preparing optically pure compounds in the pharmaceutical field, herein, enantiospecific PEM and PEC were prepared using chiral polyelectrolytes (e.g. homo-polypeptide) and their ability of chiral recognition was investigated by ATR-FTIR, UV/Vis etc.. Chiral PEM and PEC showed pronounced enantiospecificity for both small (amino acids, vitamin) and large (protein) chiral compounds. This chiral recognition is performed by a diffusion process of chiral compounds into PEM based on the structures of chiral selector (PEM, PEC) and chiral probes (chiral compounds). However, the influences, e.g. pH value, ionic strength, surface orientation etc., were found to affect significantly the enantiospecificity. Beside planar substrates, porous membranes (e.g. PTFE) were modified using chiral PEM and successfully applied in enantiospecific permeation. Additionally, protein binding properties of PEC particle dispersions or PEC particle films were also studied. Due to the properties of polyelectrolytes used for PEC (e.g. molecular weight, charge density) and proteins (e.g. isoelectric point, size, hydrophobicity), PEC showed different uptake characteristics towards different proteins. Electrostatic and hydrophobic interaction as well as counterion release force were considered as possible driving forces for protein binding.

Indiana University-Purdue University Indianapolis (IUPUI) / The proteasome is responsible for breaking down the majority of the proteins in the cell. However, a complete understanding of how this large multi-subunit protease is assembled is currently lacking. Proper and timely assembly of the proteasome is critical for the functioning of the ubiquitin-proteasome pathway, defects in which have been associated with several different cancers. A recently discovered heterodimeric proteasome assembly chaperone, Pba1p-Pba2p, has been suggested to prevent the assembly process from straying off path. Pba1p-Pba2p associates with proteasomal assembly intermediates via C-terminal HbYX motifs. The HbYX motif is a tri-peptide sequence containing a hydrophobic residue (Hb) followed by a tyrosine (Y), then any amino acid (X). This motif was originally identified in proteasomal activators, and shown to mediate the association of activators with the proteasome by inserting into intersubunit pockets on either end of the proteasome. There are seven unique intersubunit binding pockets, located between neighboring α subunits on the proteasome, to which a HbYX-containing protein can bind; which of these pockets Pba1p-Pba2p binds to remains elusive. I attempted to identify where Pba1p and Pba2p bind via a crosslinking approach. Specific residues were mutagenized to cysteines on Pba1p, Pba2p, and the individual α subunits in order to generate crosslinkable species. By exposing yeast cells expressing these crosslinkable proteins to mild oxidizing conditions, I attempted to trap the Pba1p and Pba2p α intersubunit pocket interactions. In order to optimize crosslinking conditions, the assay was modified several ways. Additionally, measures were taken to increase detection of the crosslinked species via immunoblotting. Despite the efforts to improve the crosslinking and detection, I was unable to successfully detect a crosslinked species. However, crosslinking is a reasonable method to identify the Pba1p and Pba2p proteasomal binding sites, having been successfully used to identify binding sites for other HbYX-motif-containing proteins; further assay optimization should yield Pba1p and Pba2p proteasomal crosslinks.

Matrix metalloproteinases (MMPs) network with other biological molecules to maintain the extracellular matrix (ECM) in normal physiology and perform different roles. Understanding and assigning specific role to each of 24 members of these endoproteinases is impeded because of lack of specific and efficient detection methods in biological samples. Moreover, MMP-based anti-cancer drug development has also been challenged because, currently, there is no robust methodology to distinguish the inactive pro-enzymes, active enzymes or those complexed with endogenous inhibitors in biological specimens. The objective of this project is to develop a chemical proteomics strategy based on Matrix assisted laser desorption ionization tandem mass spectrometry (MALDI-MS/MS) to help identify and discriminate the various MMP forms. Firstly, a triazine dye-based ligand immobilized on chromatography beads was utilized to assess whether it binds to recombinant human MMPs (rhMMPs). The results highlighted that the ligand interacts with latent forms of MMPs in agreement with the literature. Secondly, the potential of the ligand was assessed using MALDI-MS/MS based methodology in in vitro cancer models. Cell line culture supernatants were used in amounts to emulate the availability of tumour biopsies in clinical settings. The MS/MS spectral peaks specific to MMPs (MMP-2 and MMP- 14), and two endogenous inhibitors TIMP-1 and TIMP-2 were found in affinity chromatography eluates of cell culture supernatants with higher Mascot scores for the latter. While western blot detected MMP-2 in cell extracts, MALDI-MS/MS did not detect MMPs because of amounts below the limit of detection (LOD) of the instrument. Although the ligand was found to be interacting with MMPs and detergent-free salt elution buffers improved MALDI analysis, recovery of MMPs from biological samples was sub-optimal. The dye ligand was observed to bind other enzymes and despite various strategies to reduce non-specific binding of proteins or enable selective elution did not improve MMP enrichment. Further work using methodology described in this study is required after scaling up the MMP amounts in biological specimen and to resolve the issue of non-specific binding of proteins to the ligand by understanding its structure. / Shaukat Khanam Memorial Cancer Hospital and Research Centre, Pakistan and University of Bradford

No description available.

This dissertation details an investigation into the use of laser pulses from a titanium:sapphire regenerative amplifier laser system to vaporize analytes in ambient air for mass spectral analysis. The laser system was modified to operate in one of two distinct modes. In femtosecond (fs) mode the laser produced 2.5 mJ, ~60 fs laser pulses centered at 800 nm. In nanosecond (ns) mode the laser produced 2.4 mJ, ~10 ns laser pulses centered at 800 nm. Using appropriate optical components the laser pulse energy was attenuated to achieve pulses varying from 0.15 mJ to 2.0 mJ. Laser pulses were used to vaporize liquid and solid samples on different substrates. The laser vaporized material was captured and ionized by an electrospray source and then detected via a mass spectrometer instrument. It was discovered that samples on glass substrate could be vaporized by fs laser pulses, but not by ns laser pulses. Samples on metal substrate were successfully vaporized by both fs and ns laser pulses. Low energy ns laser pulses were less efficient than fs laser pulses of the same energy for vaporizing off metal substrate. A comparison of vaporization from aluminum, copper and stainless steel substrates revealed limited vaporization from copper by ns laser pulses. The electrospray ionization (ESI) mass spectral response of wet and dry proteins on stainless steel was similar for both fs and ns laser pulses. Experiments to test the capabilities of ns laser electrospray mass spectrometry (ns-LEMS) revealed that sample vaporization was limited to analysis on metal surfaces. This dissertation details methods for femtosecond laser electrospray ionization (fs-LEMS) to be used to quantify non-covalent protein-ligand interactions. Hen egg white lysozyme (HEWL) and N,N’,N”-triacetylchitotriose (NAG3) interactions were quantified via dissociation constant (Kd) measurements. The Kd for HEWL and N,N’,N”,N”’-tetraacetylchitotetraose (NAG4) were also measured. This dissertation also reports a miniaturized flowing atmospheric pressure afterglow (micro-FAPA) for use as an alternative ionization source of fs-laser vaporized analytes. Loratadine pills were vaporized and reacted with the gas stream from the micro-FAPA source to generate ions which were then detected by a mass analyzer. The ions detected varied in distribution as a response to the distance the sample was vaporized from the ion source. Complexed samples were tested and molecular assignments were difficult due to the numerous pathways for ion formation. The use of an ion filter to decrease the energy imparted on sample molecules during the ionization process of the micro-FAPA is also reported. / Chemistry

The mammalian protein POT1 binds to telomeric single-stranded DNA (ssDNA), protecting chromosome ends from being detected as sites of DNA damage. POT1 is composed of an N-terminal ssDNA-binding domain and a C-terminal protein interaction domain. With regard to the latter, POT1 heterodimerizes with the protein TPP1 to foster binding to telomeric ssDNA in vitro and binds the telomeric double-stranded-DNA-binding protein TRF2. We sought to determine which of these functions-ssDNA, TPP1, or TRF2 binding-was required to protect chromosome ends from being detected as DNA damage. Using separation-of-function POT1 mutants deficient in one of these three activities, we found that binding to TRF2 is dispensable for protecting telomeres but fosters robust loading of POT1 onto telomeric chromatin. Furthermore, we found that the telomeric ssDNA-binding activity and binding to TPP1 are required in cis for POT1 to protect telomeres. Mechanistically, binding of POT1 to telomeric ssDNA and association with TPP1 inhibit the localization of RPA, which can function as a DNA damage sensor, to telomeres. / Dissertation

Simulações moleculares podem fornecer informações e detalhes mecanísticos que são difíceis de obter de experimentos. No entanto, fenômenos bioquímicos como formação de complexos proteína-ligante e desenovelamento de proteína são lentos e difíceis de amostrar na escala de tempo geralmente atingida por simulações de dinâmica molecular (MD) convencionais. Esses fenômenos moleculares foram estudados aqui pela combinação de simulações de MD com diversos métodos e aproximações para aumentar a amostragem configuracional: método de energia de interação linear (LIE), a aproximação de ensemble ponderado (WE) e dinâmica molecular dirigida (SMD). Uma equação foi parametrizada para prever afinidades entre pequenas moléculas e proteínas baseada na aproximação LIE, que foca a amostragem computacional nos estados complexado e não-complexado do ligante. A flexibilidade proteica foi introduzida usando ensembles de configurações obtidos de simulações de MD. Diferentes esquemas de média foram testados para obter afinidades totais de complexos proteína-ligante, revelando que muitas configurações de complexo contribuem para as afinidades de proteínas flexíveis, enquanto as afinidades de proteínas rígidas são dominadas por uma configuração de complexo. O mutante L99A da lisozima T4 (T4L) é provavelmente a proteína mais frequentemente usada para estudar complexação de ligantes. Estruturas cristalográficas mostram que a cavidade de ligação artificial criada pela mutação é pouco acessível, portanto movimentos proteicos ou uma respiração conformacional são necessários para permitir a entrada e saída de ligantes. Simulações de MD foram combinadas aqui com a aproximação de WE para aumentar a amostragem de eventos infrequentes de saída do benzeno de T4L. Quatro possíveis caminhos foram encontrados e movimentações de alfa-hélices e cadeias laterais envolvidas na saída do ligante foram caracterizadas. Os quatro caminhos correspondem a túneis da proteína previamente observados em simulações de MD longas de T4L apo, sugerindo que a heterogeneidade de caminhos ao longo de túneis intrínsecos é explorada por pequenas moléculas para sair de cavidades de ligação enterradas em proteínas. Experimentos de microscopia de força atômica revelaram informações detalhadas do desenovelamento forçado e da estabilidade mecânica da rubredoxina, uma proteína ferro-enxofre simples. O desenovelamento completo da rubredoxina envolve a ruptura de ligações covalentes. Portanto, o processo de desenovelamento foi simulado aqui por simulações de SMD acopladas a uma descrição clássica da dissociação de ligações. A amostragem de eventos de desenovelamento forçado foi aumentada pelo uso de velocidades rápidas de esticamento. Os resultados foram analisados usando um modelo teórico válido para regimes de desenovelamento forçado lentos e rápidos. As simulações revelaram que mudanças no ponto de aplicação de força ao longo da sequência da rubredoxina levam a diferentes mecanismos de desenovelamento, caracterizados por variáveis graus de rompimento de ligações de hidrogênio e estrutura secundária da proteína. / Molecular simulations may provide information and mechanistic insights that are difficult to obtain from experiments. However, biochemical phenomena such as ligand-protein binding and protein unfolding are slow and hard to sample on the timescales usually reached by conventional molecular dynamics (MD) simulations. These molecular phenomena were studied here by combining MD simulations with several methods or approximations to enhance configurational sampling: linear interaction energy (LIE) method, weighted ensemble (WE) approach and steered molecular dynamics (SMD). An equation was parametrized to predict affinities between small molecules and proteins based on the LIE approximation, which focus computational sampling in ligand bound and unbound states. Protein flexibility was introduced by using ensembles of configurations obtained from MD simulations. Different averaging schemes were tested to obtain overall affinities for ligand-protein complexes, revealing that many bound configurations contribute to affinities for flexible proteins, while affinities for rigid proteins are dominated by one bound configuration. T4 lysozyme (T4L) L99A mutant is probably the protein most often used to study ligand binding. Crystal structures show the artificial binding cavity created by the mutation has low accessibility, so protein movements or conformational breathing are necessary to allow the entry and egress of ligands. MD simulations were combined here with the WE approach to enhance sampling of infrequent benzene unbinding events from T4L. Four possible pathways were found and motions on alpha-helices and side chains involved in ligand egress were characterized. The four pathways correspond to protein tunnels previously observed in long MD simulations of apo T4L, suggesting that pathway heterogeneity along intrinsic tunnels is explored by small molecules to egress from binding cavities buried in proteins. Previous atomic force microscopy experiments revealed detailed information on the forced unfolding and mechanical stability of rubredoxin, a simple iron-sulfur protein. Complete unfolding of rubredoxin involves rupture of covalent bonds. Thus, the unfolding process was simulated here by SMD simulations coupled to a classical description of bond dissociation. Sampling of forced unfolding events was increased by using fast pulling velocities. Results were analyzed using a theoretical model valid for both slow and fast forced unfolding regimes. Simulations revealed that changing the points of force application along the rubredoxin sequence leads to different unfolding mechanisms, characterized by variable degrees of disruption of hydrogen bonds and secondary protein structure.

This thesis describes the cloning and characterisation of a novel human gene and its protein products, which have been designated SAPK- and Ras-interacting protein (SinRIP). SinRIP shares identity with JC310, a partial human cDNA that was previously identified a candidate Ras-inhibitor (Colicelli et al., 1991, Proc Natl Acad Sci USA 88, p. 2913). In this study, it was shown that SinRIP is a member of an orthologous family of proteins that is conserved from yeast to mammals and contains proteins involved in Ras- and SAPK-mediated signalling pathways. Comparison of this family of proteins showed that human SinRIP contains a potential Ras-binding domain (RBD; residues 279-354), a PH-like domain (PHL; 376-487), and a highly conserved novel region designated the CRIM (134-265). Several other potential targeting sites, such as nuclear localisation signals and target sites for kinases, were identified within the SinRIP sequence. The human SinRIP gene is unusually large (>280 kbp) and is located on chromosome 9 at 9q34. SinRIP mRNA was detected in a wide variety of tissue-types and cell lines by RT-PCR, and the SinRIP sequences in the EST database were derived from an diverse array of tissues, suggesting a widespread or ubiquitous expression. Northern blot analysis revealed the highest levels in skeletal muscle and heart tissue. However, the steady-state levels of SinRIP mRNA vary greatly from cell to cell, and SinRIP expression is likely to be regulated at multiple post-transcriptional levels. It was shown that SinRIP mRNA is likely to be translated inefficiently by the normal cap-scanning mechanism, due to the presence of a GC-rich and structured 5’-UTR, which also contains upstream ORFs. Alternative polyadenylation signals in the SinRIP 3’-UTR can be used, resulting in the expression of short and long SinRIP mRNA isoforms. Several potential A/T-rich regulatory elements were also identified in SinRIP mRNA, which may target specific SinRIP mRNA isoforms for rapid degradation. Importantly, it was shown that SinRIP mRNA is alternatively spliced, resulting in the production of distinct SinRIP protein isoforms. Three isoforms, SinRIP2-4, were definitively identified by RT-PCR and full-length cloning. The SinRIP isoforms contain deletions in conserved regions, and are likely to have biochemical characteristics that are different to full-length SinRIP1. SinRIP2 is C-terminally truncated and lacks the PHL domain and part of the RBD, and relatively high levels of SinRIP2 expression arelikely to occur in kidneys. The RBD is disrupted in SinRIP3, but all other domains are intact, and RT-PCR analyses suggest that SinRIP3 is present in some cells at levels comparable to SinRIP1. A rabbit polyclonal antiserum against SinRIP was generated and detected endogenous SinRIP proteins. Using the anti-SinRIP antibody in immunoblots, multiple SinRIP isoforms were observed in most cell types. SinRIP1 and another endogenous SinRIP protein, likely to be SinRIP3, were detected in most cell lines, and appear to be are the major SinRIP proteins expressed in most cells. The subcellular localisation of both recombinant and endogenous SinRIP proteins was investigated by immunofluorescence assays and biochemical fractionation. Recombinant SinRIP1 protein was found in the cytoplasm and associated with the plasma membrane. In contrast, the SinRIP2 protein was predominantly nuclear, with only low-level cytoplasmic staining observed. The endogenous SinRIP proteins, likely to comprise these and other SinRIP isoforms, were found in both the nucleus and cytoplasm. SinRIP1 interacted with GTP-bound (active) Ras, but not GDP-bound (inactive) Ras, in an in vitro assay, and also co-localised with activated H- and K-Ras in cells. The binding profile observed is typical of Ras-effectors, and SinRIP did not inhibit signalling by the Ras proteins, suggesting that it is not likely to be a Ras-inhibitor. It was also shown that SinRIP1 and SinRIP2 both interact and colocalise with c-Jun NH2- terminal kinase (JNK). Both SinRIP proteins were able to recruit JNK to their respective sub-cellular compartments. These interactions suggest an adaptor role for SinRIP in the Ras and/or JNK pathways. In addition, Sam68 was isolated as a SinRIP-binding protein in a yeast two-hybrid screen. Sam68 was shown to colocalise with SinRIP2 and endogenous SinRIP proteins, but not SinRIP1. Further colocalisation studies showed that endogenous SinRIP proteins localise in nuclear structures that may be associated with pre-mRNA splicing. Likely functions for SinRIP, as indicated by experimental results and studies of the orthologues of SinRIP in other species, are discussed.

Thesis (Ph. D.)--University of Washington, 2006. / Vita. Includes bibliographical references (leaves 132-140).

The tumour suppressor p53 protein plays a central role in the DNA damage response/checkpoint pathways leading to DNA repair, cell cycle arrest, apoptosis and senescence. The activation of p53-mediated pathways is primarily facilitated by the binding of tetrameric p53 to two 'half-sites', each consisting of a decameric p53 response element (RE). Functional REs are directly adjacent or separated by a small number of 1-13 'spacer' base pairs (bp). The p53 RE is detected by exact or inexact matches to the palindromic sequence represented by the regular expression [AG][AG][AG]C[AT][TA]G[TC][TC][TC] or a position weight matrix (PWM). The use of matrix-based and regular expression pattern-matching techniques, however, leads to an overwhelming number of false positives. A more specific model, which combines multiple factors known to influence p53-dependent transcription, is required for accurate detection of the binding sites. In this thesis, we present a logistic regression based model which integrates sequence information and epigenetic information to predict human p53 binding sites. Sequence information includes the PWM score and the spacer length between the two half-sites of the observed binding site. To integrate epigenetic information, we analyzed the surrounding region of the binding site for the presence of mono- and trimethylation patterns of histone H3 lysine 4 (H3K4). Our model showed a high level of performance on both a high-resolution data set of functional p53 binding sites from the experimental literature (ChIP data) and the whole human genome. Comparing our model with a simpler sequence-only model, we demonstrated that the prediction accuracy of the sequence-only model could be improved by incorporating epigenetic information, such as the two histone modification marks H3K4me1 and H3K4me3.