Evaluated: The Structure of Sec12 Implicates Potassium Ion Coordination in Sar1 Activation.

The Structure of Sec12 Implicates Potassium Ion Coordination in Sar1 Activation.
McMahon C, Studer SM, Clendinen C, Dann GP, Jeffrey PD, Hughson FM. (2012)
J Biol Chem. in press. PMID: 23109340 DOI: 10.1074/jbc.M112.420141

This article caught my eye for two reasons: first, it maps at high resolution the likely interface between the guanine nucleotide exchange factor Sec12 and the small GTP binding protein Sar1. This interaction is critical for Sar1 activation, the essential precursor to COPII vesicle formation at the endoplasmic reticulum. Second, and where this paper is really worth a look is in the finding that this “K loop” on Sec12 that contacts Sar1 also binds a potassium ion. Furthermore, this K+ ion is essential for the catalytic activity of Sec12 towards Sar1. This paper provides a great example of the value of crystallography on proteins for which there is a very strongly predicted structure.

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