title: Dynamic conformations of nucleophosmin (NPM1) at a key monomer-monomer interface affect oligomer stability and interactions with granzyme B.
abstract: Nucleophosmin (NPM1) is an abundant, nucleolar tumor antigen with important roles in cell proliferation and putative contributions to oncogenesis. Wild-type NPM1 forms pentameric oligomers through interactions at the amino-terminal core domain. A truncated form of NPM1 found in some hepatocellular carcinoma tissue formed an unusually stable oligomer and showed increased susceptibility to cleavage by granzyme B. Initiation of translation at the seventh methionine generated a protein (M7-NPM) that shared all these properties. We used deuterium exchange mass spectrometry (DXMS) to perform a detailed structural analysis of wild-type NPM1 and M7-NPM, and found dynamic conformational shifts or local "unfolding" at a specific monomer-monomer interface which included the β-hairpin "latch." We tested the importance of interactions at the β-hairpin "latch" by replacing a conserved tyrosine in the middle of the β-hairpin loop with glutamic acid, generating Y67E-NPM. Y67E-NPM did not form stable oligomers and further, prevented wild-type NPM1 oligomerization in a dominant-negative fashion, supporting the critical role of the β-hairpin "latch" in monomer-monomer interactions. Also, we show preferential cleavage by granzyme B at one of two available aspartates (either D161 or D122) in M7-NPM and Y67E-NPM, whereas wild-type NPM1 was cleaved at both sites. Thus, we observed a correlation between the propensity to form oligomers and granzyme B cleavage site selection in nucleophosmin proteins, suggesting that a small change at an important monomer-monomer interface can affect conformational shifts and impact protein-protein interactions.
authors.affiliation: Durham VA Medical Center and Duke University Medical Center, 508 Fulton St, Durham, NC, 27705, United States of America.
authors.forename: Wei D
authors.initials: WD
authors.lastname: Duan-Porter
authors.affiliation: University of California San Diego, 9500 Gilman Drive, Room 4011, La Jolla, CA, 92093-0656, United States of America.
authors.forename: Virgil L
authors.initials: VL
authors.lastname: Woods
authors.affiliation: Johns Hopkins University School of Medicine, 5200 Eastern Avenue, Mason F. Lord Building, Center Tower, Suite 4200, Baltimore, MD, 21224, United States of America.
authors.forename: Kimberly D
authors.initials: KD
authors.lastname: Maurer
authors.affiliation: University of California San Diego, 9500 Gilman Drive, Room 4011, La Jolla, CA, 92093-0656, United States of America.
authors.forename: Sheng
authors.initials: S
authors.lastname: Li
authors.affiliation: Johns Hopkins University School of Medicine, 5200 Eastern Avenue, Mason F. Lord Building, Center Tower, Suite 4200, Baltimore, MD, 21224, United States of America.
authors.forename: Antony
authors.initials: A
authors.lastname: Rosen
mesh_terms: D000595:Amino Acid Sequence; D041961:Deuterium Exchange Measurement; D053804:Granzymes / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D013058:Mass Spectrometry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D009687:Nuclear Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D000090243:Nucleophosmin; D011485:Protein Binding; D011487:Protein Conformation; D055503:Protein Multimerization; D017386:Sequence Homology, Amino Acid
chemical_list: C000716967:NPM1 protein, human; D009687:Nuclear Proteins; D000090243:Nucleophosmin; D053804:Granzymes