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. Author manuscript; available in PMC: 2016 Jan 1.
Published in final edited form as: Curr Protein Pept Sci. 2015;16(1):31–48. doi: 10.2174/1389203716666150213160438

Figure 4. A) Schematic diagram of human MRH domain-containing proteins.

Figure 4

The location of the MRH domains (blue) is shown. The CI-MPR contains 15 contiguous MRH domains, with MRH domain 13 containing a 48-residue fibronectin type II (FnII) insert (gray). The CD-MPR and CI-MPR are type I integral membrane proteins and the location of the single transmembrane domain is shown by a vertical hatched bar. The number of amino acids in each protein, including the N-terminal signal sequence that is not shown, is indicated. The oligomeric state of the protein is listed (note: the oligomeric state of human OS-9 has not been established). GIIβ is the non-catalytic subunit of the heterodimeric glycosidase, glucosidase II, a resident protein of the ER. OS-9 and XTP3-B are also resident proteins of the ER. The γ-subunit of GlcNAc-1-phosphotransferase is the non-catalytic subunit of this hexameric glycosyltransferase localized to early Golgi compartments. CD-MPR and CI-MPR constitutively recycle between TGN, endosomes and plasma membrane. ER = endoplasmic reticulum, TGN = trans Golgi network. B) Structure-based sequence alignment. Structure-based sequence alignment of the MRH domains of bovine CD-MPR (A27068), domains 3, 5 and 9 of the bovine CI-MPR (A30788), human GII β subunit (CAA04006), human GlcNAc-1-phosphotransferase γ subunit (Q9UJJ9), the N- and C-terminal MRH domains of human XTP3-B (NP_056516), and human OS-9 (BAA24363). GII β subunit, OS-9, XTP3-B, and GlcNAc-1-phosphotransferase γ subunit contain all four essential residues for M6P recognition (Gln, Arg, Glu, and Tyr), which are shaded in red. The WW motif of OS-9 is boxed in orange. Y679, which is present in the binding pocket of domain 5, is boxed in blue. The residues known to bind the phosphate group in the CD-MPR (D103, N104, H105) and CI-MPR MRH domain 3 (S386) are boxed in red. The conserved tryptophan residue in loop C of GII β subunit is boxed in green. Residues in OS-9 predicted to prevent binding of the phosphate moiety of M6P (D182, L183) are boxed in green. The cysteine residues are shaded in yellow. The secondary structural elements of CD-MPR and OS-9 are shown, with dark blue arrows representing the β-strands and the green line representing an α-helix. Location of loops C and D are shown. PTγ = GlcNAc-1-phosphotransferase γ subunit, Erl1 = XTP3-B N-terminal MRH domain, Erl2 = XTP3-B C-terminal MRH domain