The three-dimensional structure of ricin at 2.8 A.
W.R. Montfort(Agouron Institute), J. Ernest Villafranca(University of California, San Francisco), A.F. Monzingo(University of California, San Francisco), S.R. Ernst(Agouron Institute), Betsy J. Katzin(Agouron Institute), Earl Rutenber(Agouron Institute), N.H. Xuong(University of California, San Francisco), R. Hamlin(University of California, San Francisco), Jon D. Robertus(University of California, San Francisco)
Cited by 382Open Access
Abstract
The x-ray crystallographic structure of the heterodimeric plant toxin ricin has been determined at 2.8-A resolution. The A chain enzyme is a globular protein with extensive secondary structure and a reasonably prominent cleft assumed to be the active site. The B chain lectin folds into two topologically similar domains, each binding lactose in a shallow cleft. In each site a glutamine residue forms a hydrogen bond to the OH-4 of galactose, accounting for the epimerimic specificity of binding. The interface between the A and B chains shows some hydrophobic contacts in which proline and phenylalanine side chains play a prominent role.
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