title: Identification of a pH sensor in the furin propeptide that regulates enzyme activation.
abstract: The folding and activation of furin occur through two pH- and compartment-specific autoproteolytic steps. In the endoplasmic reticulum (ER), profurin folds under the guidance of its prodomain and undergoes an autoproteolytic excision at the consensus furin site Arg-Thr-Lys-Arg107/ generating an enzymatically masked furin-propeptide complex competent for transport to late secretory compartments. In the mildly acidic environment of the trans-Golgi network/endosomal system, the bound propeptide is cleaved at the internal site 69HRGVTKR75/, unmasking active furin capable of cleaving substrates in trans. Here, by using cellular, biochemical, and modeling studies, we demonstrate that the conserved His69 is a pH sensor that regulates the compartment-specific cleavages of the propeptide. In the ER, unprotonated His69 stabilizes a solvent-accessible hydrophobic pocket necessary for autoproteolytic excision at Arg107. Profurin molecules unable to form the hydrophobic pocket, and hence, the furin-propeptide complex, are restricted to the ER by a PACS-2- and COPI-dependent mechanism. Once exposed to the acidic pH of the late secretory pathway, protonated His69 disrupts the hydrophobic pocket, resulting in exposure and cleavage of the internal cleavage site at Arg75 to unmask the enzyme. Together, our data explain the pH-regulated activation of furin and how this His-dependent regulatory mechanism is a model for other proteins.
authors.affiliation: Institut de Pharmacologie Moleculaire et Cellulaire, Valbonne, France.
authors.forename: Sylvain F
authors.initials: SF
authors.lastname: Feliciangeli
authors.forename: Laurel
authors.initials: L
authors.lastname: Thomas
authors.forename: Gregory K
authors.initials: GK
authors.lastname: Scott
authors.forename: Ezhilkani
authors.initials: E
authors.lastname: Subbian
authors.forename: Chien-Hui
authors.initials: CH
authors.lastname: Hung
authors.forename: Sean S
authors.initials: SS
authors.lastname: Molloy
authors.forename: François
authors.initials: F
authors.lastname: Jean
authors.forename: Ujwal
authors.initials: U
authors.lastname: Shinde
authors.forename: Gary
authors.initials: G
authors.lastname: Thomas
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D015153:Blotting, Western; D002460:Cell Line; D016521:Electrophoresis, Gel, Pulsed-Field; D004721:Endoplasmic Reticulum / Q000378:metabolism; D004789:Enzyme Activation; D045683:Furin / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D006863:Hydrogen-Ion Concentration; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry* / Q000378:metabolism; D034741:RNA, Small Interfering; D017386:Sequence Homology, Amino Acid
chemical_list: D010455:Peptides; D034741:RNA, Small Interfering; D045683:Furin