No description available.

Bacteria adhere despite severe mechanical perturbations. In Gram-positive bacteria, this adhesion is dependent upon a set of extracellular proteins, most notably pili, that have a unique abundance of internal disulfide, isopeptide, and thioester bonds. How these cell adhesion proteins manage to withstand such mechanical assaults, and what role these internal covalent bonds play to that end, remain open questions. Herein, we apply single-molecule force spectroscopy to delve into the mechanical behavior of three Gram-positive pilus proteins. We find that structural components of the Actinomyces oris and Corynebacterium diphtheriae pili have isopeptide-delimited extensions at extreme mechanical forces. This behavior enables efficient energy dissipation under high mechanical loads. Meanwhile, the pilus tip adhesin of Streptococcus pyogenes can covalently bind to targets via its internal thioester bond. We find that reactions with this internal thioester bond are reversible, and that both the nucleophilic bond cleavage and its spontaneous reformation are negatively force-dependent, inhibited at forces above ~30 pN and above ~7 pN, respectively. Based on these observations, we propose a model of shear-enhanced covalent adhesion for Gram-positive bacteria. Finally, we move from single-molecule characterization to application as we explore the potential of a peptide competitors to modulate the folding and function of bacterial virulence factors.

No description available.

Indiana University-Purdue University Indianapolis (IUPUI) / Alzheimer's disease (AD) is a national priority, with nearly six million Americans affected at an annual cost of $200 billion and no available cure. A better understanding of the mechanisms underlying AD is crucial to combat its high and rising incidence and burdens. Most cases of AD are thought to have a complex etiology with numerous genetic and environmental factors influencing susceptibility. Recent genome-wide association studies (GWAS) have confirmed roles for several hypothesized genes and have discovered novel loci associated with disease risk. However, most GWAS-implicated genetic variants have displayed modest individual effects on disease risk and together leave substantial heritability and pathophysiology unexplained. As a result, new paradigms focusing on biological pathways have emerged, drawing on the hypothesis that complex diseases may be influenced by collective effects of multiple variants – of a variety of effect sizes, directions, and frequencies – within key biological pathways. A variety of tools have been developed for pathway-based statistical analysis of GWAS data, but consensus approaches have not been systematically determined. We critically review strategies for genetic pathway analysis, synthesizing extant concepts and methodologies to guide application and future development. We then apply pathway-based approaches to complement GWAS of key AD-related endophenotypes, focusing on two early, hallmark features of disease, episodic memory impairment and brain deposition of amyloid-β. Using GWAS and pathway analysis, we confirmed the association of APOE (apolipoprotein E) and discovered additional genetic modulators of memory functioning and amyloid-β deposition in AD, including pathways related to long-term potentiation, cell adhesion, inflammation, and NOTCH signaling. We also identified genetic associations to amyloid-β deposition that have classically been understood to mediate learning and memory, including the BCHE gene and signaling through the epidermal growth factor receptor. These findings validate the use of pathway analysis in complex diseases and illuminate novel genetic mechanisms of AD, including several pathways at the intersection of disease-related pathology and cognitive decline which represent targets for future studies. The complexity of the AD genetic architecture also suggests that biomarker and treatment strategies may require simultaneous targeting of multiple pathways to effectively combat disease onset and progression.