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Atomic force microscopy was used to image the action of cellulolytic enzymes in situ on never-dried native cellulose films. Cellomonas fimi, CenA was used as a model enzyme for proof of concept experiments and for the identification of different enzyme action on different cellulose structures. Inactive and active Trichoderma reesei enzymes EGI and CBHI were studied to disentangle the action of the cellulose binding domain from the catalytic domain. A novel procedure, volume analysis, was developed to quantify changes in cellulose fibers as a result of this action. Volume analysis was used to compare fibers in different experiments (with different structural features and enzymes) regardless of where the change in the fiber occurred. The site-specific nature of cellulose-enzyme interactions is accessible using this analysis technique. Additionally, the reported volume change reflects a change in mass that is of interest for industrial purposes. From inactive CBHI action there was no distinguishable change between enzyme action on defect or crystalline regions of the cellulose fiber. From the active enzyme results a quantifiable degradation event was measured. Digestion was initially quick then after one hour the volume plateaued. The crystalline cellulose region plateaued at -20 ± 1% and the defect region at -31 ± 2%. The inactive EGI enzyme was found to have significant non-hydrolytic action on insoluble cellulose fibers. There was more significant swelling effect on the defect than the crystalline regions of the cellulose fiber. From the active EGI results a quantifiable degradation event was measured followed by swelling events. Degradation was initially quick with the total mass loss occurring within the first hour of the experiment. The volume then increased as the enzyme induced swelling of the fiber structure. The extent of degradation and swelling is structure limited with more disordered regions showing larger decreases in volume and predominantly crystalline regions showing mainly swelling events.

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The carcinoembryonic antigen-related cellular adhesion molecule 1 (CEACAM1) is a human receptor that facilitates adhesion with neighbouring cells, as well as with certain pathogens. CEACAM1 at the cell surface exists as a mixture of monomers and dimers in a heterogeneous distribution that is thought to regulate the balance of its functions, including those associated with pathogen binding. We used live cell fluorescence and homogeneous Förster resonance energy transfer (homo-FRET) microscopy on a combined total internal reflection fluorescence polarization (TIRFPM) confocal microscopy platform to investigate the distribution, dynamics, and monomer-dimer equilibrium of CEACAM1-4L-EYFP on live cells that were parachuted onto surfaces coated with CEACAM1-binding Neisseria gonorrhoea. Both CEACAM1-4L-EYFP and a monomeric mutant form of the receptor are rapidly recruited to bacteria and lead to downstream effector recruitment. Homo-FRET data indicate that wild-type CEACAM1-4L-EYFP was predominantly monomeric at bacterial contact sites. Preferential monomeric binding during bacterial adhesion controls the infection process.

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No description available.