Evidence for the existence of granzyme-like serine proteases in teleost cytotoxic cells.
Granzymes are granule-associated serine proteases, which are important effector molecules in NK cell and CTL functions. The granzyme family poses a perplexing problem in phylogenetics due to the lack of nonmammalian sequence information. We now report the identification of a cDNA that codes for a granzyme homologue, channel catfish granzyme-1 (CFGR-1), from nonspecific cytotoxic cells (NCC) of a teleost. NCC are the first identified and extensively studied cytotoxic cell population in teleosts. Ictalurus punctatus (channel catfish) granzyme cDNA encodes a protein with approximately 50% similarity to granzymes A and K. Highly conserved catalytic triad residues of serine proteases and other motifs common to granzymes were also identified. Conserved amino acid sequences, structure-function data available for the serine protease family, and the crystal structure of human granzyme K supported a model of CFGR-1. It suggested an Arg/Lys primary substrate specificity that is shared with granzymes A and K. Furthermore, CFGR-1 has the four conserved disulfide bonds of granzymes A, K, and M. Phylogenetic analysis suggested that this molecule is a member of the granzyme family. Expression of CFGR-1 in NCC was confirmed by RT-PCR analysis. Presence of a granzyme-like molecule that might play an important role in the effector functions of NCC indicates that cell-mediated immunity with granule exocytosis and Fas pathways have been conserved for more than 300 million years.
Praveen
Kesavannair
K
Department of Medical Microbiology and Parasitology, College of Veterinary Medicine, University of Georgia, Agriculture Drive, Athens, GA 30602, USA.
Evans
Donald L
DL
Jaso-Friedmann
Liliana
L
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D018076:DNA, Complementary; D006801:Humans; D007059:Ictaluridae; D007694:Killer Cells, Natural / Q000201:enzymology*; D008969:Molecular Sequence Data; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D012697:Serine Endopeptidases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
D018076:DNA, Complementary; D012697:Serine Endopeptidases