Detection of disulfide linkage by chemical derivatization and mass spectrometry

OH1 from Orf Virus: A New Tyrosine Phosphatase that Displays Distinct Structural Features and Triple Substrate Specificity

Viral tyrosine phosphatases such as VH1 from Vaccinia and Variola virus are recognized as important effectors of host-pathogen interactions. While proteins sharing sequence to VH1 have been identified in other viruses, their structural and functional characterization is not known. In this work, we determined the crystal structure of the VH1 homolog in the Orf virus, herein named OH1. Similarly to Variola and Vaccinia VH1, the structure of OH1 shows a dimer with the typical dual-specificity phosphatase fold. In contrast to VH1, the OH1 dimer is covalently stabilized by a disulfide bond involving residue Cys15 in the N-terminal helix alpha-1 of both monomers, and Cys15 is a conserved residue within the Parapoxvirus genus. The in vitro functional characterization confirms that OH1 is a dual-specificity phosphatase and reveals its ability to dephosphorylate phosphatidylinositol 3,5-bisphosphate, a new activity potentially relevant in phosphoinositide recycling during virion maturation.

Modification of Cysteine

This unit describes a number of methods for modifying cysteine residues of proteins and peptides. A general procedure for alkylation of cysteine residues in a protein of known size and composition with haloacyl reagents or N-ethylmaleimide (NEM) is presented, and alternate protocols describe similar procedures for use when the size and composition are not known and when only very small amounts of protein are available. Alkylations that introduce amino groups using bromopropylamine and N-(iodoethyl)-trifluoroacetamide are also presented. Two procedures that are often used for subsequent sequence analysis of the protein, alkylation with 4-vinylpyridine and acrylamide, are described, and a specialized procedure for 4-vinylpyridine alkylation of protein that has been adsorbed onto a sequencing membrane is also presented. Reversible modification of cysteine residues by way of sulfitolysis is described, and a protocol for oxidation with performic acid for amino acid compositional analysis is also provided. Gentle oxidation of cysteine residues to disulfides by exposure to air is described. Support protocols are included for recrystallization of iodoacetic acid, colorimetric detection of free sulfhydryls, and desalting of modified samples. © 2017 by John Wiley & Sons, Inc.