5aex | pdb_00005aex
Crystal structure of Saccharomyces cerevisiae Mep2
Structural highlights
Function[MEP2_YEAST] Transporter for ammonium (both charged and uncharged NH3 and NH4) to use as a nitrogen source. The affinity of MEP2 is about twenty times higher than that of MEP1. MEP3 has the lowest affinity. Under ammonium limitation acts as an ammonium sensor, generating a signal that leads to pseudohyphal growth.[1] [2] [3] [4] Publication Abstract from PubMedMep2 proteins are fungal transceptors that play an important role as ammonium sensors in fungal development. Mep2 activity is tightly regulated by phosphorylation, but how this is achieved at the molecular level is not clear. Here we report X-ray crystal structures of the Mep2 orthologues from Saccharomyces cerevisiae and Candida albicans and show that under nitrogen-sufficient conditions the transporters are not phosphorylated and present in closed, inactive conformations. Relative to the open bacterial ammonium transporters, non-phosphorylated Mep2 exhibits shifts in cytoplasmic loops and the C-terminal region (CTR) to occlude the cytoplasmic exit of the channel and to interact with His2 of the twin-His motif. The phosphorylation site in the CTR is solvent accessible and located in a negatively charged pocket approximately 30 A away from the channel exit. The crystal structure of phosphorylation-mimicking Mep2 variants from C. albicans show large conformational changes in a conserved and functionally important region of the CTR. The results allow us to propose a model for regulation of eukaryotic ammonium transport by phosphorylation. Structural basis for Mep2 ammonium transceptor activation by phosphorylation.,van den Berg B, Chembath A, Jefferies D, Basle A, Khalid S, Rutherford JC Nat Commun. 2016 Apr 18;7:11337. doi: 10.1038/ncomms11337. PMID:27088325[5] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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