title: Structural basis of the pH-dependent assembly of a botulinum neurotoxin complex.
abstract: Botulinum neurotoxins (BoNTs) are among the most poisonous biological substances known. They assemble with non-toxic non-hemagglutinin (NTNHA) protein to form the minimally functional progenitor toxin complexes (M-PTC), which protects BoNT in the gastrointestinal tract and releases it upon entry into the circulation. Here we provide molecular insight into the assembly between BoNT/A and NTNHA-A using small-angle X-ray scattering. We found that the free form BoNT/A maintains a pH-independent conformation with limited domain flexibility. Intriguingly, the free form NTNHA-A adopts pH-dependent conformational changes due to a torsional motion of its C-terminal domain. Once forming a complex at acidic pH, they each adopt a stable conformation that is similar to that observed in the crystal structure of the M-PTC. Our results suggest that assembly of the M-PTC depends on the environmental pH and that the complex form of BoNT/A is induced by interacting with NTNHA-A at acidic pH.
authors.affiliation: Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Stanford University, Menlo Park, CA 94025, USA. Electronic address: tmatsui@slac.stanford.edu.
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Matsui
authors.affiliation: Department of Physiology and Biophysics, University of California, Irvine, CA 92697, USA.
authors.forename: Shenyan
authors.initials: S
authors.lastname: Gu
authors.affiliation: Department of Physiology and Biophysics, University of California, Irvine, CA 92697, USA.
authors.forename: Kwok-Ho
authors.initials: KH
authors.lastname: Lam
authors.affiliation: Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Stanford University, Menlo Park, CA 94025, USA.
authors.forename: Lester G
authors.initials: LG
authors.lastname: Carter
authors.affiliation: Institut für Toxikologie, Medizinische Hochschule Hannover, Carl-Neuberg-Strasse 1, 30625 Hannover, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Rummel
authors.affiliation: Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Stanford University, Menlo Park, CA 94025, USA.
authors.forename: Irimpan I
authors.initials: II
authors.lastname: Mathews
authors.affiliation: Department of Physiology and Biophysics, University of California, Irvine, CA 92697, USA. Electronic address: r.jin@uci.edu.
authors.forename: Rongsheng
authors.initials: R
authors.lastname: Jin
mesh_terms: D001905:Botulinum Toxins / Q000737:chemistry* / Q000378:metabolism; D018360:Crystallography, X-Ray; D006863:Hydrogen-Ion Concentration; D009498:Neurotoxins / Q000737:chemistry* / Q000378:metabolism; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D053838:Scattering, Small Angle; D014961:X-Ray Diffraction
chemical_list: C088300:NTNH protein, Clostridium botulinum; D009498:Neurotoxins; D001905:Botulinum Toxins
keywords: X-ray scattering; botulinum neurotoxin; neurotoxin-associated proteins; non-toxic non-hemagglutinin; progenitor toxin complex