2m19 | pdb_00002m19
Solution structure of the Haloferax volcanii HVO 2177 protein
Structural highlights
FunctionSAMP3_HALVD Functions as a protein modifier covalently attached to lysine residues of substrate proteins. The protein modification process is termed sampylation and involves the formation of an isopeptide bond between the SAMP3 C-terminal glycine carboxylate and the epsilon-amino group of lysine residues on target proteins. Seems to be able to form polymeric chains with itself at Lys-18, Lys-55 and Lys-62, similar to ubiquitin and other ubiquitin-like proteins. SAMP3 appears not to serve as a proteolytic signal in the cell to target proteins for degradation by proteasomes. May regulate molybdenum cofactor (MoCo) biosynthesis by inhibiting the activity of MPT synthase MoaE under aerobic conditions, providing a hierarchy of oxygen use prior to that of alternative electron acceptors such as DMSO.[1] [2] Publication Abstract from PubMedThe discovery of ubiquitin-like small archaeal modifier protein 2 (SAMP2) that forms covalent polymeric chains in Haloferax volcanii has generated tremendous interest in the function and regulation of this protein. At present, it remains unclear whether the Hfx. volcanii modifier protein SAMP1 has such polyubiquitinating-like activity. Although SAMP1 and SAMP2 use the same conjugation machinery to modify their target proteins, each can impart distinct functional consequences. To better understand the mechanism of SAMP2 conjugation, we have sought to characterize the biophysical and structural properties of the protein from Hfx. volcanii. SAMP2 is only partially structured under mesohalic solution conditions and adopts a well-folded compact conformation in the presence of 2.5M of NaCl. Its 2.3-A-resolution crystal structure reveals a characteristic alpha/beta central core domain and a unique beta-hinge motif. This motif anchors an unusual C-terminal extension comprising the diglycine tail as well as two lysine residues that can potentially serve to interlink SAMP2 moieties. Mutational alternation of the structural malleability of this beta-hinge motif essentially abolishes the conjugation activity of SAMP2 in vivo. In addition, NMR structural studies of the putative ubiquitin-like protein HVO_2177 from Hfx. volcanii show that like SAMP1, HVO_2177 forms a classic beta-grasp fold in a salt-independent manner. These results provide insights into the structure-function relationship of sampylating proteins of fundamental importance in post-translational protein modification and environmental cues in Archaea. Crystal structure of the ubiquitin-like small archaeal modifier protein 2 from Haloferax volcanii.,Li Y, Maciejewski MW, Martin J, Jin K, Zhang Y, Maupin-Furlow JA, Hao B Protein Sci. 2013 Jul 2. doi: 10.1002/pro.2305. PMID:23821306[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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