High-speed atomic force microscopy reveals strongly polarized movement of clostridial collagenase along collagen fibrils.

Bacterial collagenases involved in donor infection are widely applied in many fields due to their high activity and specificity; however, little is known regarding the mechanisms by which bacterial collagenases degrade insoluble collagen in host tissues. Using high-speed atomic force microscopy, we simultaneously visualized the hierarchical structure of collagen fibrils and the movement of a representative bacterial collagenase, Clostridium histolyticum type I collagenase (ColG), to determine the relationship between collagen structure and collagenase movement. Notably, ColG moved ~14.5 nm toward the collagen N terminus in ~3.8 s in a manner dependent on a catalytic zinc ion. While ColG was engaged, collagen molecules were not only degraded but also occasionally rearranged to thicken neighboring collagen fibrils. Importantly, we found a similarity of relationship between the enzyme-substrate interface structure and enzyme migration in collagen-collagenase and DNA-nuclease systems, which share a helical substrate structure, suggesting a common strategy in enzyme evolution.

High-speed atomic force microscopy reveals structural dynamics of amyloid ß1-42 aggregates.

Aggregation of amyloidogenic proteins into insoluble amyloid fibrils is implicated in various neurodegenerative diseases. This process involves protein assembly into oligomeric intermediates and fibrils with highly polymorphic molecular structures. These structural differences may be responsible for different disease presentations. For this reason, elucidation of the structural features and assembly kinetics of amyloidogenic proteins has been an area of intense study. We report here the results of high-speed atomic force microscopy (HS-AFM) studies of fibril formation and elongation by the 42-residue form of the amyloid ß-protein (Aß1-42), a key pathogenetic agent of Alzheimer's disease. Our data demonstrate two different growth modes of Aß1-42, one producing straight fibrils and the other producing spiral fibrils. Each mode depends on initial fibril nucleus structure, but switching from one growth mode to another was occasionally observed, suggesting that fibril end structure fluctuated between the two growth modes. This switching phenomenon was affected by buffer salt composition. Our findings indicate that polymorphism in fibril structure can occur after fibril nucleation and is affected by relatively modest changes in environmental conditions.