Keller A, Chavez JD, Felt KC, Bruce JE. Prediction of an Upper Limit for the Fraction of Interprotein Cross-Links in Large-Scale In Vivo Cross-Linking Studies.
J Proteome Res 2019;
18:3077-3085. [PMID:
31267744 DOI:
10.1021/acs.jproteome.9b00189]
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Abstract
Chemical cross-linking and mass spectrometry is of growing use for establishment of distance constraints on protein conformations and interactions. Whereas intraprotein cross-links can arise from proteins in isolation, interprotein cross-links reflect proximity of two interacting proteins in the sample. Prediction of expected ratios of the number of interprotein to intraprotein cross-links is hindered by lacking comprehensive knowledge on the interactome network and global occupancy levels for all interacting complex subunits. Here we determine the theoretical number of possible inter- and intraprotein cross-links in available PDB structures of proteins bound in complexes to predict a maximum expected fraction of interprotein cross-links in large scale in vivo cross-linking studies. We show how the maximum fraction can guide interpretation of reported interprotein fractions with respect to the extent of sample protein binding, comparing whole cell and lysate cross-linked samples as an example. We also demonstrate how an observation of interprotein cross-link fractions greater than the maximum value can result from the presence of false positive cross-links which are predominantly interprotein, their number estimable from the observed surplus fraction of interprotein cross-links.
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