title: The dimeric transmembrane domain of prolyl dipeptidase DPP-IV contributes to its quaternary structure and enzymatic activities.
abstract: Dipeptidyl peptidase IV (DPP-IV) is a drug target in the treatment of human type II diabetes. It is a type II membrane protein with a single transmembrane domain (TMD) anchoring the extracellular catalytic domain to the membrane. DPP-IV is active as a dimer, with two dimer interacting surfaces located extracellularly. In this study, we demonstrate that the TM of DPP-IV promotes DPP-IV dimerization and rescues monomeric DPP-IV mutants into partial dimers, which is specific and irreplaceable by TMs of other type II membrane proteins. By bioluminescence resonance energy transfer (BRET) and peptide electrophoresis, we found that the TM domain of DPP-IV is dimerized in mammalian cells and in vitro. The TM dimer interaction is very stable, based on our results with TM site-directed mutagenesis. None of the mutations, including the introduction of two prolines, resulted in their complete disruption to monomers. However, these TM proline mutations result in a significant reduction of DPP-IV enzymatic activity, comparable to what is found with mutations near the active site. A systematic analysis of TM structures deposited in the Protein Data Bank showed that prolines in the TM generally produce much bigger kinking angles than occur in nonproline-containing TMs. Thus, the proline-dependent reduction in enzyme activity may result from propagated conformational changes from the TM to the extracellular active site. Our results demonstrate that TM dimerization and conformation contribute significantly to the structure and activity of DPP-IV. Optimal enzymatic activity of DPP-IV requires an optimal interaction of all three dimer interfaces, including its TM.
authors.affiliation: Division of Biotechnology and Pharmaceutical Research, National Health Research Institutes, Zhu Nan town, Miaoli County, Taiwan, Republic of China.
authors.forename: Kuei-Min
authors.initials: KM
authors.lastname: Chung
authors.forename: Jai-Hong
authors.initials: JH
authors.lastname: Cheng
authors.forename: Ching-Shu
authors.initials: CS
authors.lastname: Suen
authors.forename: Chih-Hsiang
authors.initials: CH
authors.lastname: Huang
authors.forename: Cheng-Han
authors.initials: CH
authors.lastname: Tsai
authors.forename: Li-Hao
authors.initials: LH
authors.lastname: Huang
authors.forename: Yi-Rong
authors.initials: YR
authors.lastname: Chen
authors.forename: Andrew H-J
authors.initials: AH
authors.lastname: Wang
authors.forename: Weir-Torn
authors.initials: WT
authors.lastname: Jiaang
authors.forename: Ming-Jing
authors.initials: MJ
authors.lastname: Hwang
authors.forename: Xin
authors.initials: X
authors.lastname: Chen
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D018819:Dipeptidyl Peptidase 4 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D055503:Protein Multimerization; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment
chemical_list: D018819:Dipeptidyl Peptidase 4