Protein Science, Vol 7, Issue 8 1781-1788, Copyright © 1998 by Cold Spring Harbor Laboratory Press

ARTICLE

The role of the 6 lysines and the terminal amine of Escherichia coli single-strand binding protein in its binding of single-stranded DNA

J. CHEN, D. L. SMITH and M. A. GRIEP
Department of Chemistry, University of Nebraska-Lincoln, Lincoln, Nebraska 68588-0304

Differential chemical modification of the lysines and amino-terminus of Escherichia coli single-strand binding (SSB) protein was used to determine their roles in the binding of SSB to single-stranded DNA (ssDNA). A combination of isotope labeling and mass spectrometry was used to determine the rates at which SSB was acetylated by acetic anhydride. First, SSB was labeled by deuterated acetic anhydride for given lengths of time in the presence or absence of single-stranded ssDNA. Then, the protein was denatured and completely acetylated by nondeuterated acetic anhydride. Enzymatic digests of the completely acetylated, isotopically labeled SSB were analyzed by electrospray ionization mass spectrometry. The intensities of the deuterated and nondeuterated forms of acetylated peptides provided accurate quantification of the reactivity of the amines in native SSB, either free or bound to ssDNA. Acetylation rate constants were determined from time course measurements. In the absence of ssDNA, the terminal {alpha}-amine of SSB was 10-fold more reactive than Lys residues at positions 43, 62, 73, and 87. The reactivities of Lys 7 and 49 were much lower yet, suggesting that they have very limited access to solution under any condition. In the presence of ssDNA, the reactivities of the amino-terminus and Lys residues 43, 62, 73, and 87 were reduced by factors of 3.7-25, indicating that the environments around all of these amines is substantially altered by binding of SSB to ssDNA. Three of these residues are located near putative ssDNA binding sites, whereas Lys 87 is located at the monomer-monomer interface.
CiteULike    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?

This article has been cited by other articles:

				E. A. Worthey, A. Schnaufer, I. S. Mian, K. Stuart, and R. Salavati Comparative analysis of editosome proteins in trypanosomatids Nucleic Acids Res., November 15, 2003; 31(22): 6392 - 6408. [Abstract] [Full Text] [PDF]

				E. M. Hyland, L. F. Rezende, and C. C. Richardson The DNA Binding Domain of the Gene 2.5 Single-stranded DNA-binding Protein of Bacteriophage T7 J. Biol. Chem., February 21, 2003; 278(9): 7247 - 7256. [Abstract] [Full Text] [PDF]

				L. F. Rezende, T. Hollis, T. Ellenberger, and C. C. Richardson Essential Amino Acid Residues in the Single-stranded DNA-binding Protein of Bacteriophage T7. IDENTIFICATION OF THE DIMER INTERFACE J. Biol. Chem., December 20, 2002; 277(52): 50643 - 50653. [Abstract] [Full Text] [PDF]