title: Identification of phosphorylation sites in Hansenula polymorpha Pex14p by mass spectrometry.
abstract: Pex14p is a peroxisomal membrane protein that is involved in both peroxisome biogenesis and selective peroxisome degradation. Previously, we showed that Hansenula polymorpha Pex14p was phosphorylated in vivo. In this study, we identified its phosphorylation site by mass spectrometry. Recombinant His-tagged Pex14p (H6-Pex14p) was overexpressed and purified from the yeast. The protein band corresponding to H6-Pex14p was in-gel digested with trypsin and subjected to LC/MS. As a result of LC/MS, Thr(248) and Ser(258) were identified as the phosphorylated sites. To confirm the phosphorylation sites and explore its functions, we made Ala mutants of the candidate amino acids. In the western blot analysis with anti-Pex14p, S258A mutant gave doublet bands while wild type (WT) and T248A mutants gave triplet bands. Moreover, the double mutant (T248A/S258A) gave a single band. WT and all mutant Pex14p labeled with [(32)P] orthophosphate were immunoprecipitated and analyzed by autoradiography. The phosphorylation of Pex14p was suppressed in S258A mutant, but enhanced in T248A mutant compared to WT. Moreover, the phosphorylated Pex14p was not detected in the T248A/S258A double mutant. All mutants were able to grow on methanol and their matrix proteins (alcohol oxidase and amine oxidase) were mostly localized in peroxisomes. Furthermore all mutants showed selective degradation of peroxisome like WT during the glucose-induced macropexophagy.
authors.affiliation: Laboratory of Cellular and Molecular Biology, Department of Veterinary Science, Graduate School of Life and Environmental Sciences, Osaka Prefecture University, 1-58 Rinku Ourai Kita, Izumisano, Osaka 598-8531, Japan.
authors.forename: Katsuhiro
authors.initials: K
authors.lastname: Tanaka
authors.forename: Maiko
authors.initials: M
authors.lastname: Soeda
authors.forename: Yoichiro
authors.initials: Y
authors.lastname: Hashimoto
authors.forename: Shigeo
authors.initials: S
authors.lastname: Takenaka
authors.forename: Masayuki
authors.initials: M
authors.lastname: Komori
keywords: AMO, amine oxidase; AOX, alcohol oxidase; Hansenula polymorpha; Mass spectrometry; PNS, post nuclear supernatant; PTS, peroxisomal targeting signal; PVDF, polyvinylidene difluoride; Peroxisome; Pex14p; Phosphorylation; SDS–PAGE, sodium dodecyl sulfate poly-acrylamide gel electrophoresis; TCA, trichloroacetic acid