Comparative Analysis of The Self- and Co-assembly of Type-I and Type-III Collagen
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Collagen represents the most abundant protein family in the human body which forms 30% of the total protein. Among different types, type-I and type-III are the two most abundant, respectively, in the heterotypic fibril structure. Although many tissues in the human body have a heterotypic form of co-assembled two or more types of collagens, not much is known concerning the heterotypic assembly of two or more types of collagens. Therefore, the purpose of this study is to investigate the characteristics of the co-assembly process of the two main types of collagen. Collagen, which is a major component of an Extracellular Matrix (ECM) protein, also has a self-assembly ability in vitro, and the resulting matrices are used as scaffolds for cell-biological applications, templates for microelectronic applications, coating materials for non-biological surfaces for enhanced bio-compatibility. The assembly process is, so far, mostly monitored turbidimetrically in solution. In this study, by using atomic force microscopy(AFM), custom image analysis, and kinetic modeling, we study the homotypic and the heterotypic assembly of type-I and type-III collagen on muscovite and phlogopite mica surfaces with varying concentrations and ratios of the two collagen types. We found that when assembled individually, type-I collagen nucleates and assembles faster than type-III, and forms thicker fibrils. When the two collagens co-assemble, the fibril thickness and growth rate decrease as the fraction of type-III collagen increases. However, the fibril nucleation rate depends non-monotonically on the type-III fraction, being the highest for an intermediate mixture of types-I and III collagens. These results can be understood based on their amino acid composition, where type-I collagen, being more hydrophobic, nucleates fibrils fast and grows in both longitudinal and lateral directions. In contrast, the more hydrophilic character of type-III collagen limits the lateral growth of fibrils, which in turn makes more monomers available to nucleate additional fibrils. These results demonstrate how subtle differences in physico-chemical properties of similar molecules can be used to fine-tune their assembly behavior.
Eryilmaz, Esma (2015). Comparative Analysis of The Self- and Co-assembly of Type-I and Type-III Collagen. Doctoral dissertation, Texas A&M University. Available electronically from