An Interprotein Co-S Coordination Complex in the B-12-Trafficking Pathway

• Type of Material: Article
• Authors: Zhu Li, University of Michigan; Romila Mascarenhas, University of Michigan; Umar T Twahir, Emory University; Albert Kallon, University of Michigan; Aniruddha Deb, University of Michigan; Madeline Yaw, University of Michigan; James Penner-Hahn, University of Michigan; Markos Koutmos, University of Michigan; Kurt Warncke, Emory University; Ruma Banerjee, University of Michigan
• Language: English
• Date: 2020-09-23
• Publisher: AMER CHEMICAL SOC
• Publication Version: Author Accepted Manuscript (After Peer Review)
• Copyright Statement: © 2020 American Chemical Society
• Final Published Version (URL): http://dx.doi.org/10.1021/jacs.0c06590
• Title of Journal or Parent Work: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
• Volume: 142
• Issue: 38
• Start Page: 16334
• End Page: 16345
• Grant/Funding Information: This work was supported in part by grants from the National Institutes of Health (R01-DK045776 to RB, R01-DK054514 to KW), the American Heart Association (19POST34370113 to RM) and from the National Science Foundation (NSF-CHE 1945174 to MK).
• Keywords: PROTEIN; MMACHC; VITAMIN-B-12; Science & Technology; CBLC; GLUTATHIONE; Chemistry, Multidisciplinary; DOMAIN; Chemistry; TRAFFICKING CHAPERONE BCBLC; GLUTATHIONYLCOBALAMIN; B-12 TRAFFICKING; CRYSTAL-STRUCTURE; Physical Sciences

Abstract

The CblC and CblD chaperones are involved in early steps in the cobalamin trafficking pathway. Cobalamin derivatives entering the cytoplasm are converted by CblC to a common cob(II)alamin intermediate via glutathione-dependent alkyltransferase or reductive elimination activities. Cob(II)alamin is subsequently converted to one of two biologically active alkylcobalamins by downstream chaperones. The function of CblD has been elusive although it is known to form a complex with CblC under certain conditions. Here, we report that CblD provides a sulfur ligand to cob(II)alamin bound to CblC, forming an interprotein coordination complex that rapidly oxidizes to thiolato-cob(III)alamin. Cysteine scanning mutagenesis and EPR spectroscopy identified Cys-261 on CblD as the sulfur donor. The unusual interprotein Co-S bond was characterized by X-ray absorption spectroscopy and visualized in the crystal structure of the human CblD thiolato-cob(III)alamin complex. Our study provides insights into how cobalamin coordination chemistry could be utilized for cofactor translocation in the trafficking pathway.