期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2007
卷号：104
期号：44
页码：17311-17316
DOI：10.1073/pnas.0703228104
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：The structure of intrinsic factor (IF) in complex with cobalamin (Cbl) was determined at 2.6-A resolution. The overall fold of the molecule is that of an {alpha}6/{alpha}6 barrel. It is a two-domain protein, and the Cbl is bound at the interface of the domains in a base-on conformation. Surprisingly, two full-length molecules, each comprising an {alpha}- and a [beta]-domain and one Cbl, and two truncated molecules with only an {alpha}- domain are present in the same asymmetric unit. The environment around Cbl is dominated by uncharged residues, and the sixth coordinate position of Co2+ is empty. A detailed comparison between the IF-B12 complex and another Cbl transport protein complex, trans-Cbl-B12, has been made. The pH effect on the binding of Cbl analogues in transport proteins is analyzed. A possible basis for the lack of interchangeability of human and rat IF receptors is presented.
关键词：incomplete dimer ; x-ray ; cobalt ; transport protein ; glycoprotein
