Dataset Information

NefCD4AP2 Complex Crosslinking with DSSO for Integrative Structure Determination

ABSTRACT: Objective: HIV-1 Nef suppresses immune surveillance mechanisms to promote viral pathogenesis. Cellular receptor CD4 is essential for HIV entry into host cells, though becomes problematic at later stages in the virus replication cycle. CD4 at the plasma membrane is targeted by Nef for endocytosis and lysosomal degradation via recruitment of clathrin adaptor complex 2 (AP2 complex). Our goal is to use cross-linking mass spectrometry and integrative modeling to aid in structure determination of flexible portions of the Nef-CD4-AP2 complex. Methods: We use disuccinimidyl sulfoxide (DSSO), a MS-cleavable, bifunctional amine-reactive small molecule, to cross-link proximal Lys residues or N-termini of a purified reconstituted Nef-CD4 C-terminal domain fusion protein bound to the AP2Δμ2-CTD complex. Cross-linked proteins were separated by SDS-PAGE, excised from the gel and digested with trypsin. The resulting peptides were analyzed by specialized LC-MS3 experiments for identification of cross-linked residues using MSconvert (to obtain individual MS2 and MS3 level mgf files), ProteinProspector (to obtain peptide identification results files), and XLTools (to identify cross-linked peptides from results, MS2, and MS3 files). Additional scripts were used to summarize cross-linked results. Results: We find that an intricate combination of conformational changes occurs in both Nef and AP2 to enable CD4 binding and downregulation. A pocket on Nef previously identified as crucial for recruiting class I MHC is also responsible for recruiting CD4, revealing a potential approach to inhibit two of Nef’s activities and sensitize the virus to immune clearance.

INSTRUMENT(S): LTQ Orbitrap Elite

ORGANISM(S): Homo Sapiens (human) Human Immunodeficiency Virus 1

SUBMITTER: Robyn Kaake

LAB HEAD: Nevan J. Krogan

PROVIDER: PXD019338 | Pride | 2021-09-09

REPOSITORIES: Pride

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Publications

Structural basis of CD4 downregulation by HIV-1 Nef.

Kwon Yonghwa Y Kaake Robyn M RM Echeverria Ignacia I Suarez Marissa M Karimian Shamsabadi Mohammad M Stoneham Charlotte C Ramirez Peter W PW Kress Jacob J Singh Rajendra R Sali Andrej A Krogan Nevan N Guatelli John J Jia Xiaofei X

Nature structural & molecular biology 20200727 9

The HIV-1 Nef protein suppresses multiple immune surveillance mechanisms to promote viral pathogenesis and is an attractive target for the development of novel therapeutics. A key function of Nef is to remove the CD4 receptor from the cell surface by hijacking clathrin- and adaptor protein complex 2 (AP2)-dependent endocytosis. However, exactly how Nef does this has been elusive. Here, we describe the underlying mechanism as revealed by a 3.0-Å crystal structure of a fusion protein comprising Ne ...[more]

PMID: 32719457

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Project description:Over the past few decades cross-linking mass spectrometry (XLMS) has become a powerful tool for identification of protein-protein interactions and for gaining insight into the structures of proteins in living cells, tissues, and organelles. The development of new crosslinkers, enrichment strategies and data acquisition methods led to the establishment of numerous new software tools specifically for the analysis and interpretation of cross-linking data. We previously published one of these tools called MS Annika, a cross-linking search engine which can accurately identify cross-linked peptides in MS2 spectra from a variety of different MS-cleavable crosslinkers. In this publication we present an updated MS Annika and a new search algorithm that additionally supports processing of data from MS2-MS3-based approaches and identification of peptides from MS3 spectra. In the new MS2-MS3 search algorithm, MS3 spectra are matched to their corresponding precursor doublet peak in the MS2 scan to identify the crosslink modification and the monoisotopic peptide mass. This information is then used to adjust the MS3 spectra for search with MS Amanda, our in-house developed peptide search engine, to identify the cross-linked peptides. Peptides that are identified in the MS2 scan and one or more of the associated product MS3 scans are re-scored with a novel scoring function to reflect the increased confidence. Finally, the detected cross-links are validated by estimating the false discovery rate (FDR) using a target-decoy approach. We evaluated the MS3-search-capabilities of MS Annika on five different datasets covering a variety of experimental approaches and compared it to XlinkX and MaXLinker, two other cross-linking search engines that support MS3 crosslink identification. Three of the datasets were benchmark datasets of synthetic peptides that allow calculation of an experimentally validated FDR, and we show that MS Annika detects up to 4 times more true unique crosslinks than MaXLinker and up to 35% more than XlinkX while simultaneously yielding less false positive hits and therefore a more accurate FDR than the other two search engines. Additionally, for the other two datasets we could show that MS Annika finds between 74% to 2.5 times more crosslinks at 1% estimated FDR and reveals protein-protein interactions that are not detected by either XlinkX or MaXLinker.

Dataset Information

NefCD4AP2 Complex Crosslinking with DSSO for Integrative Structure Determination

Publications

Structural basis of CD4 downregulation by HIV-1 Nef.

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