Animal collagen

Collagen is one of the hall-marks of the animals, and is an essential structural protein that plays a key role in such areas as ligament and the skin. It seems, moreover, to be unique to the animals, or is it? Its construction is relatively simple and employs three intertwined helices of amino-acids with characteristic triplet repeats of Glycine-Proline-Y (where Y is another amino acid); in addition hydroxyproline is also widely used.

Bacterial collagen

Intriguingly in a bacterium, and specifically in the wall of anthrax spores a protein occurs that is very reminiscent of collagen, again showing a triplet repeat but instead of G-P-Y, it is P-T-G (i.e. Proline-Threonine-Glycine). So is the evolution of collagen so surprising? Most biologists would regard it as “one of those things”, more or less a fluke. We beg to differ. Animals, where-ever they are, need to call upon a structural protein and it seems they may inevitably call upon collagen.

Another twist in the collagen story is evidence of its export from animals (most likely a vertebrate) to a cyanobacterium (Trichodesmium erythraeum) that lives in the ocean. Interestingly, it forms vast blooms whose aggregation is evidently assisted by the collagen to help keep the cells together.