EXPRESSION, CRYSTALLIZATION, AND PRELIMINARY-X-RAY ANALYSIS OF A SIALIC ACID-BINDING FRAGMENT OF SIALOADHESIN IN THE PRESENCE AND ABSENCE OF LIGAND

Sialoadhesin is a macrophage-restricted cell surface receptor, consist ing of 17 immunoglobulin domains, which mediates cell adhesion via the recognition of specific sialylated glycoconjugates. A functional frag ment of sialoadhesin, comprising the N-terminal immunoglobulin domain, has been expressed in Chinese hamster ovary cells as both native (SnD 1) and selenomethionyl (Se-SnD1) stop protein. The successful producti on of 86% selenomethionine-incorporated protein represents a rare exam ple of production of selenium-labeled protein in mammalian cells. SnD1 and Se-SnD1 have been crystallized in the absence of ligand, and SnD1 has also been crystallized in the presence of its ligand 2,3 sialylla ctose. The ligand-free crystals of SnD1 and Se-SnD1 were isomorphous, of space group P3(1)21 or P3(2)21, with unit cell dimensions a = b = 3 8.9 Angstrom, c = 152.6 Angstrom, alpha = beta = 90 degrees, gamma = 1 20 degrees, and diffracted to a maximum resolution of 2.6 Angstrom. Co crystals containing 2,3 sialyllactose diffracted to 1.85 Angstrom at a synchrotron source and belong to space group P2(1)2(1)2(1), with unit cell dimensions a = 40.9 Angstrom, b = 97.6 Angstrom, c = 101.6 Angst rom, alpha = beta = gamma = 90 degrees.