Limulus protein

The determination of the endotoxin with limulus amebocyte lysate (LAL) is based on gel formation of a mixture consisting of a solution of endotoxin of Gram-negative bacteria with a solution of lysate. The extent and speed of the reaction depend on the endotoxin concentration, pLL, and temperature. The reaction requires the presence of certain cations, a proclotting enzymes system, and clottable protein, which are produced by lysate. 

Another remarkable example is extension of the acrosomal process from a sperm cell of the horseshoe crab Limulus polyphemus at fertilization. A bundle of actin filaments in a crystalline state lies coiled around the base of the nucleus. At fertilization the bundle uncoils and slides through a tunnel in the nucleus to form a 60 pm-long acrosomal process within a few seconds. The uncoiled bundle is also crystalline. The coiled bundle is apparently overtwisted and an actin crosslinking protein scrum mediates the conformational alteration that takes place.339 A somewhat related process maybe involved in contraction of bacteriophage tails (pp. 363,364)... 

The deoxy forms of hemocyanins are colorless, as a result of their 3d ° dicopper(I) centers. Although chemical and x-ray absorption spectroscopic studies had shed considerable light on the nature of the deoxy-He dicopper binding site, there now exist two x-ray crystal structures, the first on the the spiny lobster He, Panulirus interruptus [23], and a recent one of the horseshoe crab Limulus II protein [24], The structures exhibit rather different active-site characteristics, and since the former was crystallized at low pH and possesses rather odd copper coordination, the latter Limulus II structure is probably representative. It indicates that the two Cu(I) ions are 4.6 A apart, each found in a trigonal-planar coordination environment with Cu-NMs bond distances of about 2.0 A (Figure 1). Intersubunit 02 binding cooperative effects are probably initiated and trans-... 

Hazes B et al (1993) Crystal structure of deoxygenated Limulus polyphemus subunit II hemo-cyanin at 2.18 A resolution clues for a mechanism for allosteric regulation. Protein Sci 2 597-619 PDBID lNOL... 

Hoess, A., Watson, S., Siber, G.R., Liddington, R. Crystal structure of an endotoxin-neutralizing protein from the horseshoe crab, Limulus anti-LPS factor, at 1.5 A resolution. EMBO J 12 (1993) 3351-3356. 

Vanadate(V) and GTP-y-S, a hydrolysis resistant analog of GTP, have recently been shown to excite photoreceptors of the horseshoe crab Limulus in the dark and have been used to help elucidate the chemical steps which are involved in the phototransduction process153. The results suggest that vanadate binds to a guanyl nucleotide binding protein which activates adenylate cyclase. 

Way M, Sanders M, Garcia C et al. Sequence and domain organization of scruin, an actin-cross-linking protein in the acrosomal process of Limulus sperm. J Cell Biol 1995 128(l-2) 51-60. 

Levin, J. Bang, F.B. Clottable protein in Limulus its localization and kinetics of its coagulation by endotoxin. 

The stability of the black copper complex and its tendency to form soluble, highly colored complexes with amines (and also denatured albumen) indicates that the compound we have in hand is involved in the union of the copper to the protein in hemocyanin. The function of the prosthetic group thus appears to be the same as that of protoporphyrin in hemoglobin, namely, to provide a basis for a very stable metallic complex. Beyond this analogy, however, there seems to be little or no chemical relationship between the prosthetic groups in limulus hemocyanin and hemoglobin. It should be noted that since limulus hemocyanin differs markedly in its copper content from the hemocyanin of other species,2 the conclusions we have drawn do not necessarily apply to the nature of the prosthetic group in the other hemocyanins. 

Fig. 28.8 The structure of deoxyhaemocyanin from the spiny lobster Panulirus interruptus) (a) the backbone of the protein chain and the positions of the two Cu(I) centres, and (b) the active site in which the two Cu(I) centres are bound by histidine residues, (c) The 02-binding site in oxyhaemocyanin from the Atlantic horseshoe crab (Limulus polyphemus). Hydrogen atoms are omitted colour code Cu, brown C, grey O, red N, blue.

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