Investigating the Role of the Collagen Protein in Trichodesmium erythraeum.

摘要

Collagen molecules are structural in nature and primarily found in eukaryotic, multicellular organisms. The collagen protein family is diverse and its membership is continually expanding as new collagen-like molecules are identified. Although previously believed to be limited to eukaryotes, collagen-like proteins have been identified in various prokaryotic organisms. Identification of collagen in unicellular eukaryotes and prokaryotes has opened discussion on the function of these collagens and their role in the emergence of multicellularity. Recently, a collagen-like gene was identified in the marine cyanobacterium, Trichodesmium erythraeum. T. erythraeum is a colonial, filamentous cyanobacterium found in tropical and subtropical oligotrophic oceans. Based on the known function of collagen proteins, it was hypothesized that the collagen protein encoded in the T. erythraeum genome functioned to provide structural integrity for normal growth and survival of T. erythraeum. The collagen protein, named TrpA, was found to be both transcribed and translated at all phases of growth though there is a marked increase in transcription during the logarithmic phase, and a significantly increased amount of protein expressed during both the logarithmic and stationary phase. Immunofluorescent labeling of the TrpA protein revealed that the collagen protein is expressed in the septa between cells along the filament. Additionally, TrpA can be seen localizing to the division septa forming during intercalary cell division. Collagenase treatment of T. erythraeum trichomes exhibited fragmentation of the cells along the filament. Using phylogenetic analysis, structural modeling and circular dichroism, it was confirmed that the protein being expressed belongs to the collagen family, specifically exhibiting characteristics of non-fibrillar collagens. Scanning electron microscopy revealed that TrpA is also being expressed entirely on the surface of the trichomes. While working towards developing a TrpA knockout, it was revealed that T. erythraeum is likely naturally transformable. Based on the results found in this study, it is clear that the collagen protein identified in the genome of T. erythraeum is involved in maintaining cell-cell adhesion of the cells along the filament. The expression of TrpA on the surface of trichomes indicates that this protein may also be involved in the adherence of trichomes within a colony.