In looking at the morphology of a few of the innate immune proteins (collectins) I have been trying to sort out whether the collagen-like domains have a “similar” flexibility, or tendency to “bend”.  I was hoping to find some differences, but if they exist I think they will be small (though small does not preclude significance). I found one publication that showed rotary shadowed molecules of CL-43, or SP-D and bovine conglutinin… hopefully  at equivalent magnifications (as stated). The micrograph showed trimers of CL-42, dodecamers of SP-D and conglutinin.  There is a slight curvature to the collagen-like domain (which is invariably NOT shown in diagrams) which is pretty consistent in micrographs from many publications.

The purpose is to determine if the slight curvature has bearing on how the SP-D multimers associate, and how their trimeric arms are positioned in “fuzzyballs”.  The arc angles are shown for each quadrant of SP-D and conglutinin below. THe CL-43 is not shown because it apparently does not form dodecamers.

I am also linking a site for calculating arc angles and other measures of circles as a really helpful teaching website.