Congratulations to Sam Allen, who has been selected as one of the recipients of the Department of Chemistry’s Graduate Student Merit Fellowships.
Native mass spectrometry and ion mobility spectrometry were used to investigate the gas-phase structures of selected cations and anions of proteins and protein complexes with masses ranging from 6–468 kDa. Under the same solution conditions, the average charge states observed for all native-like anions were less than those for the corresponding cations. Using an RF-confining drift cell, similar collision cross sections were measured in positive and negative ion mode suggesting that anions and cations have very similar structures. This result suggests that for protein and protein complex ions within this mass range, there is no inherent benefit to selecting a specific polarity for capturing a more native-like structure. For peptides and low-mass proteins, polarity and charge-state dependent structural changes may be more significant. The charged-residue model is most often used to explain the ionization of large macromolecules based on the Rayleigh limit, which defines the upper limit of charge that a droplet can hold. Because ions of both polarities have similar structures and the Rayleigh limit does not depend on polarity, these results cannot be explained by the charged-residue model alone. Rather, the observed charge-state distributions are most consistent with charge-carrier emissions during the final stages of analyte desolvation, with lower charge-carrier emission energies for anions than the corresponding cations. These results suggest that the observed charge-state distributions in most native mass spectrometry experiments are determined by charge-carrier emission processes; although the Rayleigh limit may determine the gas-phase charge states of larger species, e.g., virus capsids.
Effects of Polarity on the Structures and Charge States of Native-like Proteins and Protein Complexes in the Gas Phase Samuel J. Allen, Alicia M. Schwartz, Matthew F. Bush. Anal. Chem. 2013, 85, 12055–12061. (Link|PUBMED)
Congratulations to Chrissy Stachl, who has been awarded the Pfizer – La Jolla Academic and Industrial Relations (AIR) 2013-2014 Diversity Research Fellowship in Chemistry! This highly selective Fellowship will support her research this academic year.
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Prof. Bush just returned from the Department of Chemistry at Mercer University, where he presented a seminar and met with undergraduate students. He thanks the American Society for Mass Spectrometry for support and Prof. Kathryn Kloepper for hosting his visit.
Prof. Bush will present the following seminars this November:
- Department of Chemistry, Pacific Lutheran University, Tacoma, WA, 11/25/13. MFB thanks Prof. Tina Saxowsky for hosting this visit.
- Joint Chemistry Seminar, Claremont McKenna, Harvey Mudd, Pomona, Pitzer, and Scripps Colleges, Claremont, CA, 11/19/13. MFB thanks the American Society for Mass Spectrometry for travel support and Prof. Aaron Leconte for hosting this visit.
- Department of Chemistry & Biochemistry, Northern Illinois University, DeKalb, IL, 11/11/13. MFB thanks Prof. Victor Ryzhov and Prof. Marc Adler for hosting this visit.
- Department of Chemistry, Mercer University, Macon, GA, 11/1/13. MFB thanks the American Society for Mass Spectrometry for travel support and Prof. Kathryn Kloepper for hosting this visit.
The type II secretion system (T2SS), a multiprotein machinery spanning two membranes in Gram-negative bacteria, is responsible for the secretion of folded proteins from the periplasm across the outer membrane. The critical multidomain T2SS assembly ATPase GspEEpsE had not been structurally characterized as a hexamer. Here, four hexamers of Vibrio cholerae GspEEpsE are obtained when fused to Hcp1 as an assistant hexamer, as shown with native mass spectrometry. The enzymatic activity of the GspEEpsE-Hcp1 fusions is ∼20 times higher than that of a GspEEpsE monomer, indicating that increasing the local concentration of GspEEpsE by the fusion strategy was successful. Crystal structures of GspEEpsE-Hcp1 fusions with different linker lengths reveal regular and elongated hexamers of GspEEpsE with major differences in domain orientation within subunits, and in subunit assembly. SAXS studies on GspEEpsE-Hcp1 fusions suggest that even further variability in GspEEpsE hexamer architecture is likely.
Hexamers of the Type II Secretion ATPase GspE from Vibrio cholerae with Increased ATPase Activity Connie Lu, Stewart Turley, Samuel T. Marionni, Young-Jun Park, Kelly K. Lee, Marcella Patrick, Ripal Shah, Maria Sandkvist, Matthew F. Bush, Wim G.J. Hol. Structure 2013, 21, 1707–1717. (Link|PUBMED)
Prof. Bush will present the following talks:
- Native Mass Spectrometry: Ionization, Ion Mobility, and the Mammalian Circadian Clock. Matthew F. Bush. Greater Boston Mass Spectrometry Discussion Group, Boston, MA, 9/19/13. (Additional Information|Flyer)
- Department of Chemistry & Chemical Biology, Northeastern University, Boston, MA, 9/18/13.
- Ion mobility mass spectrometry of a mammalian circadian clock protein complex reveals a ligand-dependent conformational switch. Samuel T. Marionni, Weiman Xing, Ning Zheng, Matthew F. Bush. American Chemical Society National Meeting, Indianapolis, IN, 9/11/13. (Additional Information)
Congratulations to Alicia Schwartz, who recently accepted a position with the Infectious Disease Research Institute! We’ll miss you!
The Bush Lab and collaborators are presenting the following talks at the Cascadia Proteomics Symposium, which takes place at the Institute for Systems Biology in Seattle from July 15-16.
- Ion Mobility Mass Spectrometry of Native Protein Complex Anions Samuel J. Allen, Alicia M. Schwartz, Matthew F. Bush (Tuesday @ 10:15 AM)
- Selected Cation to Anion Proton Transfer Kenneth J. Laszlo, Matthew F. Bush (Tuesday @ 10:50 AM)
- Assembly of the Type II Secretion ATPase Probed by Native Mass Spectrometry Samuel T. Marionni, Connie Lu, Stewart Turley, Young-Jun Park, Kelly Lee, Marcella Patrick, Ripal Shah, Maria Sandkvist, Wim G.J. Hol, Matthew F. Bush (Tuesday @ 1:00 PM)
Matt Bush is the recipient of the 2013 ASMS Research Award, which promotes academic research by young scientists in mass spectrometry.