Biochemical properties and cDNa cloning of two new lectins from the plasmaof Tachypleus tridentatus - Tachypleus plasma lectin 1 and 2+

A Sepharose CL-4B-binding protein, Tachypleus plasma lectin 1 (TPL-1), and a lipopolysaccharide (LPS)binding protein, Tachypleus plasma lectin-2 (TPL- 2), have been isolated from the plasma of Tachypleus tri-dentatus and bioch emically characterized, Each protein is coded by a homologous family of mul tigenes, TPL-1 binds to Sepharose CL-4B and was eluted with buffer containi ng 0.4 M GlcNAc, The deduced amino acid sequence of TPL-1 consisted of 232 amino acids with an N-glycosylation site, Asn-Gly-Ser at residues 74-76. It shares a 65% sequence identity and similar internal repeats of about 20 am ino acid motifs with tachylectin-1. Tachylectin-1 was identified as a lipop olysaccharideagarose binding nonglycosylated protein from the amebocytes of T, tridentatus, TPL-8 was eluted from the LPS-Sepbarose CL-4B affinity col umn in buffer containing 0.4 M GlcNAc and 2 M KCI, The deduced amino acid s equence of TPL-2 consisted of 128 amino acids with an N-glycosylation site, Asn-Cys-Thr, at positions 3-5, It shares an 80% sequence identity with tac hylectin-3, isolated from the amebocytes of T, tridentatus, TPL-2 purified by LPS-affinity column from the plasma predominantly exists as a dimer of a glycoprotein with an apparent molecular mass of 36 kDa, Tachylectin-3 is a n intracellular nonglycosylated protein that also exists as a dimer in solu tion with an apparent molecular mass of 29 kDa, It recognizes Gram-negative bacteria through the 0-antigen of LPS, Western blot analyses showed that, in the plasma, TPL-1 and TPL-2 exist predominantly as oligomers with molecu lar masses above 60 kDa, They both bind to Gram-positive and Gram-negative bacteria, and this binding is inhibited by GlcNAc, Possible binding site of TPL-1 and TPL-8 to the bacteria could be at the NAc moiety of GlcNAc-MurNA c of the peptidoglycan, The physiological function of TPL-1 and TPL-2 is mo st likely related to their ability to form a cluster of interlocking molecu les to immobilize and entrap invading organisms.