THE BEHAVIOR OF CONCANAVALIN A WITH CROSS-LINKING REAGENT IN THE ANHYDROUS ACETONITRILE. Minxie Qian, Qichen Huang and Yuoqi Tang, Department of Chemistry Peking University, Beijing 100871, P.R. CHINA

Concanavalin A is a saccharide-binding protein from Jack Bean. Well-ordered crystals were soaked in mother liquor of 1.2 M phosphate ( pH 6.45 ) with 7.5% gluteraldehyde solution for 30 min. After washing cross-linked crystal with pure water 5 times, the crystal named as CON III, was soaked in the anhydrous acetonitrile for 5 min. The X-ray diffraction data of CON III was collected to 2.8A resolution. For comparison, X-ray diffraction data were subsequently collected for both native crystal (named as CON I) and two additional cross-linked crystals ( named as CON II and CON IV). The CON II was only washed 5 times with pure water after cross-linked. After the CON IV was treated as CON III, it was soaked in pure water for 1 h. The crystals diffracted to 1.8A for CON I, 1.9A for CON II and 1.9A for CON VI, respectively. The cell dimensions of CON II and CON VI remain relatively constant with respect to the native CON I. But the cell dimensions of CON III were dramatically changed, which were decreased about 5 A in both a axis and b axis, and was increased 1 A in c axis. The changes of cell dimension are depended on the arrangement of molecule in the crystal. The major feature of secondary structure of Concanavalin A is that the polypeptide chain only contains several beta-strands, which parallel each other along c axis.

Several deviations in the regions of C-terminal and flexible loops between beta-strands are observed by superposition of main chain of CON III with native CON I. The segment corresponding to the four residues peptide chain (between PHE233 and ASN237) in the C-terminal adopts a distinctly different position in CON III. The maximum mainchain movement is about 14 A at ASN237. The configurations of both CON II and CON VI are as same as the one of Native CON I. It is shown that the changed configuration of segments effected by the anhydrous acetonitrile are rapidly recovered in the pure water. The refinement of cross-linked crystals are in the process.