Antibacterial 15-kDa protein isoforms (p15s) are members of a novel family of leukocyte proteins.
We have previously described the isolation and initial characterization of functionally distinct 15-kDa protein isoforms (p15s) from rabbit polymorphonuclear leukocytes (PMN) that bind with high affinity to Escherichia coli and modulate the antibacterial actions of other leukocyte proteins on this Gram-negative bacterium. We now report the cloning and sequencing of two distinct cDNAs from a rabbit bone marrow library that encode p15s differing at only 2 residues (His-3, Arg-88 versus Arg-3, Trp-88). Tryptophan-directed chemical cleavage of two isoforms purified from a single rabbit confirms the existence of multiple isoforms with distinct function and primary structure in a single rabbit. The p15 cDNAs encode putative signal sequences and studies of cellular and subcellular localization indicate that the p15s are granule-associated proteins of PMN. Both purified isoforms bind avidly to lipopolysaccharide (LPS), the major component of the Gram-negative bacterial outer membrane. Analysis of the deduced primary structures of the p15s reveals homology to three other leukocyte proteins: CAP-18, an 18-kDa LPS-binding protein from rabbit PMN, pro-indolicidin, a 16-kDa precursor of an antibacterial peptide of bovine PMN, and cathelin, an 11-kDa cysteine protease inhibitor from porcine leukocytes, suggesting the existence of a novel family of leukocyte proteins with LPS-binding, antimicrobial, and protease-inhibitory activities.
Levy
O
O
Department of Microbiology, New York University School of Medicine, New York 10016.
Weiss
J
J
Zarember
K
K
Ooi
C E
CE
Elsbach
P
P
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001770:Blood Bactericidal Activity; D001798:Blood Proteins / Q000235:genetics* / Q000378:metabolism; D002417:Cattle; D003001:Cloning, Molecular; D004247:DNA; D008070:Lipopolysaccharides / Q000378:metabolism; D008969:Molecular Sequence Data; D009504:Neutrophils / Q000378:metabolism*; D011817:Rabbits; D017386:Sequence Homology, Amino Acid
D001798:Blood Proteins; D008070:Lipopolysaccharides; D004247:DNA