INTERACTION OF INTERCELLULAR ADHESION MOLECULE-1 (ICAM-1) AND HUMAN RHINOVIRUS (HRV) AND THE ROLE OF CHARGE Prasanna R. Kolatkar, Jordi Bella, Wai-ming Lee^*, Roland Rueckert^* and Michael G. Rossmann Department of Biological Sciences, Purdue University, W. Lafayette, IN 47906 ^*Institute of Molecular Virology, University of Wisconsin, Madison, WI 53706.

Intercellular Adhesion Molecule-1 (ICAM-1) is the receptor used by the majority of human rhinoviruses (HRVs). We have previously reported a cryo-electron microscopy reconstruction of the ICAM-1:HRV complex (PNAS, 1992) which shows the general features of the binding. Well-diffracting crystals of ICAM-1 expressed in bacullovirus are now being used for crystallographic studies. Nevertheless the crystals have somewhat variable cell constants which change by as much as 10Å and make MIR phasing problematic. The variability in cell constants is likely attributed to the significant amount of glycosylation.We (Chris Marlor, Jeff Greve; Bayer Inc., W. Haven , CT 06516) have introduced one selenomethionine into ICAM-1 to allow MAD phasing.In addition we are using MAD data collection at the absorption edges of heavy atom derivatives to obtain phase information. We will report the progress of the structure determination of ICAM-1 and its relevance to understanding virus-receptor binding interactions.

The charge surface potentials of several human rhinoviruses have been calculated using X-ray coordinates of HRVs. We have employed site-directed mutagenesis of certain charged residues within the canyon and which overlap with the ICAM-1 footprint determined from the EM reconstruction. The results are consistent with the observed HRV:ICAM-1 interactions.