Another group of proteins identified are those suggested to be involved
in the immune response, including a cyclophilin, two cystatins
and a lipopolysaccharide and beta-1,3-glucan-binding protein (LPSBP).
Cyclophilin (n1, n3) belongs to a family of proteins found in all living
organisms, and exhibit peptidyl-prolyl cis–trans isomerase activity
during protein folding [62,63]. Cyclophilins are diverse in their subcellular
localizations, and include secretion pathway-targeted members,
such as the presently identified gastrolith cyclophilin. In the horseshoe
crab, a marine arthropod, a 27 kDa protein designated cyclophilin
G was identified in hemocyte secretory granules containing antimicrobial
peptides that undergo exocytosis upon stimulation by
bacterial-derived substances [64]. Apart from a strong similarity to
cyclophilin B, the horseshoe crab protein also exhibited isomerase
activity.