Purification and partial characterization of a β-1,3-glucan-binding-protein membrane receptor from blood cells of the crayfish Pacifastacus leniusculus

Authors


Correspondence to K. Söderhäll, Department of Physiological Botany, University of Uppsala, Box 540, S-751 21 Uppsala, Sweden

Abstract

A receptor for the 100 kDa β-1,3-glucan-binding protein [Duvic, B. and Söderhäll, K. (1990) J. Biol. Chem. 265, 9327–9332] has been purified from hemocyte membranes of the crayfish Pacifastacus leniusculus. The purification was achieved by DEAE-cellulose chromatography of detergentsolubilized membranes. The receptor had an apparent molecular mass of 350 kDa when subjected to native polyacrylamide-gel electrophoresis and was composed of two non-covalently associated subunits of about 230 kDa and 90 kDa, as judged by SDS/polyacrylamide-gel electrophoresis or two-dimensional electrophoresis. The receptor could only bind the β-1,3-glucan-binding protein if this protein had previously reacted with a β-1,3-glucan, laminarin, and the binding site was located on the 230 kDa subunit. The binding of laminarin-treated β-1,3-glucan-binding protein to its receptor was a saturable process and binding data indicated a single high-affinity-binding site with a Kd of 0.35 ± 0.15 μM as determined by Scatchard analysis. The receptor had a requirement for divalent cations and a pH optimum of 6.5 for binding the laminarin-treated β-1,3-glucan-binding protein. Laminarin, as well as oligosaccharides such as D-glucose, sialic acid, N-acetyl glucosamine or methyl-α-D-mannoside, could not affect the binding of the β-1,3-glucan-binding protein to its receptor.

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