Structural and functional properties of a novel serine protease inhibiting peptide family in arthropods.
Recently, several arthropod peptides that belong to a new serine protease inhibitor family were discovered. Three members (HI, PMP-D2=LMCI-1 and PMP-C=LMCI-2) were isolated from the migratory locust, Locusta migratoria. Five additional members (SGPI-1-5) were identified in the desert locust Schistocerca gregaria, and a heterodimeric serine protease inhibitor (pacifastin) was isolated from the hemolymph of the crayfish Pacifastacus leniusculus. The light chain of pacifastin constitutes the inhibitory subunit that has nine cysteine-rich domains (PLDs) that are homologous with the locust inhibitors. These locust inhibitors and PLDs share a conserved array of six cysteine residues (Cys-Xaa(9-12)-Cys-Asn-Xaa-Cys-Xaa-Cys-Xaa(2-3)-Gly-Xaa(3-4)-Cys-Thr-Xaa(3)-Cys), which are involved in an identical disulfide bridge pattern (Cys(1)-Cys(4), Cys(2)-Cys(6), Cys(3)-Cys(5)). The solution structures of LMCI-1 and LMCI-2 showed a similar, compact, globular folding, which is unique within the group of the small 'canonical' inhibitors. Moreover, the reactive site, including the P1-P'1 bond was thoroughly investigated by means of synthetic variants. However, the biological function(s) of the locust inhibitors is (are) not fully understood. LMCI-1 and LMCI-2 were shown to inhibit the endogenous proteolytic activating cascade of prophenoloxidase. Northern blot analysis indicated that the genes encoding the SGPI precursors are differentially expressed in a time-, stage- and hormone-dependent manner.
Simonet
Gert
G
Laboratory for Developmental Physiology and Molecular Biology, K.U. Leuven, Belgium. gert.simonet@bio.kuleuven.ac.be
Claeys
Ilse
I
Broeck
Jozef Vanden
JV
D000595:Amino Acid Sequence; D000818:Animals; D003400:Astacoidea; D001665:Binding Sites; D015152:Blotting, Northern; D002918:Chymotrypsin / Q000737:chemistry; D047169:Cyclotides; D003545:Cysteine / Q000737:chemistry; D004220:Disulfides; D006110:Grasshoppers; D019476:Insect Proteins / Q000737:chemistry* / Q000145:classification / Q000502:physiology*; D007700:Kinetics; D008969:Molecular Sequence Data; D005810:Multigene Family; D010455:Peptides / Q000737:chemistry; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000737:chemistry / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D015842:Serine Proteinase Inhibitors / Q000494:pharmacology*; D013997:Time Factors
D002918:Chymotrypsin; D047169:Cyclotides; D003545:Cysteine; D004220:Disulfides; D019476:Insect Proteins; D010455:Peptides; D011506:Proteins; D015842:Serine Proteinase Inhibitors; C113210:LOC126284306 protein, Schistocerca gregaria; C113212:SGPI III protein, Schistocerca gregaria; C106709:pacifastin; C072986:PMP-D2 peptide, insect; C072987:PMP-C peptide, insect