About

William T. Wickner is a Professor of Biological Chemistry at the University of California, Los Angeles, within the Department of Biological Chemistry. He holds the academic rank of Emeritus Professor / Researcher and has been associated with UCLA since at least 1974. His office is located at 615 Charles E Young Drive South, 310 BSRB, Los Angeles, California. The department offers various resources including Biological Chemistry Courses, Imaging Facility, Consignment Stockroom, and Graduate Programs in Bioscience. His professional focus involves research in biological chemistry, contributing to the understanding of cellular and molecular mechanisms.

Research topics

• Biology
• Cell biology
• Biochemistry
• Chemistry
• Biophysics

Selected publications

• BPS2025 - Sec18 side-loading is essential for universal SNARE recycling across cellular contexts

  Biophysical Journal · 2025-02-01

  article
  PublisherDOI

• BPS2025 - Sec18 side-loading is essential for universal SNARE recycling across cellular contexts

  Biophysical Journal · 2025-02-01

  article
  PublisherDOI

• SNARE disassembly requires Sec18/NSF side loading

  Nature Structural & Molecular Biology · 2025-07-02 · 4 citations

  articleOpen access

  SNARE (soluble N-ethylmaleimide-sensitive factor (NSF) attachment protein receptor) proteins drive membrane fusion at different cell compartments as their core domains zipper into a parallel four-helix bundle. After fusion, these bundles are disassembled by the AAA+ (ATPase associated with diverse cellular activities) protein Sec18/NSF and its adaptor Sec17/α-SNAP to make them available for subsequent rounds of membrane fusion. SNARE domains are often flanked by C-terminal transmembrane or N-terminal domains. Previous structures of the NSF-α-SNAP-SNARE complex revealed binding to the D1 ATPase pore, posing a topological constraint as SNARE transmembrane domains would prevent complete substrate threading as suggested for other AAA+ systems. Using mass spectrometry in yeast cells, we show N-terminal SNARE domain interactions with Sec18, exacerbating this topological issue. We present cryo-electron microscopy (cryo-EM) structures of a yeast SNARE complex, Sec18 and Sec17 in a nonhydrolyzing condition, which show SNARE Sso1 threaded through the D1 and D2 ATPase rings of Sec18, with its folded, N-terminal Habc domain interacting with the D2 ring. This domain does not unfold during Sec18/NSF activity. Cryo-EM structures under hydrolyzing conditions revealed substrate-released and substrate-free states of Sec18 with a coordinated opening in the side of the ATPase rings. Thus, Sec18/NSF operates by substrate side loading and unloading topologically constrained SNARE substrates.

  PublisherOA PDFDOI

• Functional Assembly of the Qc-SNARE with Sec18 and Sec17 on Membranes

  bioRxiv (Cold Spring Harbor Laboratory) · 2025-10-21

  preprintOpen accessSenior authorCorresponding

  Abstract Yeast vacuolar fusion is driven by Sec17, Sec18, SNAREs (R, Qa, Qb, Qc) and HOPS, a catalyst of SNARE assembly. Qc, the only vacuolar SNARE that is not membrane-anchored, has a unique path of assembly with other fusion catalysts. Qc is the only SNARE which binds Sec17 with high affinity. Sec18 confers a high affinity for Qc (but not Qb) on HOPS-dependent fusion, but it has been unclear how Sec18 acts. The membrane complex of Sec17 and Sec18 bind Qc to form a membrane:Sec18:Sec17:Qc complex. Sec18 ATP hydrolysis, though dispensable for fusion, provides a measure of the physical and functional interactions between Qc, Sec17, Sec18, and membranes. Each binary interface in this quaternary complex regulates Sec18 ATPase and fusion. Qc is better than other SNAREs, alone or in combination, for stimulating ATP hydrolysis. We propose a working model in which membrane-bound Qc:Sec17:Sec18 associates with the trans complex of HOPS:R:QaQb, displacing HOPS while providing both Qc for complete SNARE zippering and localized Sec17 apolar loops, the twin driving forces for fusion.

  PublisherOA PDFDOI

• Functional assembly of the Qc-SNARE with Sec18 and Sec17 on membranes

  Molecular Biology of the Cell · 2025-11-19

  articleOpen accessSenior author

  Yeast vacuolar fusion is driven by Sec17, Sec18, SNAREs of four families (R [Nyv1], Qa [Vam3], Qb [Vti1], Qc [Vam7]) and HOPS, a catalyst of SNARE assembly. Qc, the only vacuolar SNARE that is not membrane-anchored, has a unique path of assembly with other fusion catalysts. Qc is the only SNARE that binds Sec17 with high affinity. Sec18 confers a high affinity for Qc (but not Qb) on HOPS-dependent fusion, but it has been unclear how Sec18 acts. The membrane complex of Sec17 and Sec18 binds Qc to form a membrane:Sec18:Sec17:Qc complex. Sec18 ATP hydrolysis, though dispensable for fusion, provides a measure of the physical and functional interactions between Qc, Sec17, Sec18, and membranes. Each binary interface in this quaternary complex regulates Sec18 ATPase and fusion. Qc is better than other SNAREs, alone or in combination, for stimulating ATP hydrolysis. We propose a working model in which membrane-bound Qc:Sec17:Sec18 associates with the trans complex of HOPS:R:QaQb, displacing HOPS while providing both Qc for complete SNARE zippering and localized Sec17 apolar loops, the twin driving forces for fusion.

  PublisherOA PDFDOI

• Sec18 ATP hydrolysis selectively releases Sec17 from <i>trans</i>-SNARE complexes, inhibiting membrane fusion

  Molecular Biology of the Cell · 2025-05-07 · 2 citations

  articleSenior author

  Intracellular membrane fusion is catalyzed by SNAREs, Rabs, SM proteins, tethers, Sec18/NSF, and Sec17/SNAP. Fusion has two engines, completion of SNARE zippering (without needing Sec17/Sec18) and Sec17/Sec18 (which need SNAREs but not energy from their complete zippering). We have reconstituted membrane fusion with purified vacuolar proteins to address three questions: 1) whether Sec18 ATP hydrolysis affects fusion, 2) whether Sec17 and Sec18 only promote fusion with mutant SNAREs or also work with wild-type SNAREs, and 3) whether Sec17 and Sec18 can separately promote fusion. We find that 1) Sec18 ATP hydrolysis blocks fusion at limiting Sec17 levels by releasing Sec17 without concomitant trans-SNARE complex disassembly. At higher (physiological) Sec17 levels, or without ATP hydrolysis, fusion prevails over Sec17 release. 2) With entirely wild-type SNAREs and with unimpeded SNARE zippering, Sec17, Sec18, and either ATP or a nonhydrolyzable ATP analogue stimulate fusion. 3) Sec17 and Sec18 work together but can act independently. Fusion blocked by impaired zippering can be restored by concentrated Sec17 alone (but not by Sec18), while fusion inhibited by stiff fatty acyl chains is partially restored by Sec18 alone (but not by Sec17). Optimal fusion needs zippering, Sec17, and Sec18.

  PublisherDOI

• SNARE disassembly requires Sec18/NSF side-loading

  bioRxiv (Cold Spring Harbor Laboratory) · 2024-09-01 · 2 citations

  preprintOpen access

  SNARE proteins drive membrane fusion at different cell compartments as their core domains zipper into a parallel four-helix bundle. After fusion, these bundles are disassembled by the AAA+ protein Sec18/NSF and its adaptor Sec17/α-SNAP to make them available for subsequent rounds of membrane fusion. SNARE domains are often flanked by C-terminal transmembrane or N-terminal domains. Previous structures of the NSF-α-SNAP-SNARE complex revealed binding to the D1 ATPase pore, posing a topological constraint as SNARE transmembrane domains would prevent complete substrate threading as suggested for other AAA+ systems. Using mass-spectrometry in yeast cells, we show N-terminal SNARE domain interactions with Sec18, exacerbating this topological issue. We present cryo-EM structures of a yeast SNARE complex, Sec18, and Sec17 in a non-hydrolyzing condition, which show SNARE Sso1 threaded through the D1 and D2 ATPase rings of Sec18, with its folded, N-terminal Habc domain interacting with the D2 ring. This domain does not unfold during Sec18/NSF activity. Cryo-EM structures under hydrolyzing conditions revealed substrate-released and substrate-free states of Sec18 with a coordinated opening in the side of the ATPase rings. Thus, Sec18/NSF operates by substrate side-loading and unloading topologically constrained SNARE substrates.

  PublisherOA PDFDOI

• After their membrane assembly, Sec18 (NSF) and Sec17 (SNAP) promote membrane fusion

  Molecular Biology of the Cell · 2024-10-30 · 6 citations

  articleOpen accessSenior author

  The energy that drives membrane fusion can come from either complete SNARE zippering, from Sec17 and Sec18, or both. Sec17 and Sec18 initially form a complex which binds membranes. Sec17, Sec18, and the apolarity of a loop on the N-domain of Sec17 are required for their interdependent membrane association. To determine whether Sec18 and the Sec17 loop apolarity are still required for fusion after their membrane arrival, a hydrophobic transmembrane (TM) anchor was affixed to the N-terminus of Sec17, forming TM-Sec17. Fusion without energy from complete SNARE zippering requires Sec18 as well as either Sec17 or TM-Sec17. Even without the need for membrane targeting, the TM-Sec17 apolar loop strongly stimulates Sec17/18-driven fusion. Thus, Sec18 and the Sec17 apolar loop are first required for membrane targeting, and once bound, drive rapid fusion. Each of these variables—the absence or presence of Sec17, its N-loop apolarity, addition or omission of Sec18, and unimpeded or diminished energy from SNARE zippering—has almost no effect on the amount of trans-SNARE complex, but instead regulates the capacity of docked membranes to fuse.

  PublisherOA PDFDOI

• Membrane fusion reactions limited by defective SNARE zippering or stiff lipid fatty acyl composition have distinct requirements for Sec17, Sec18, and adenine nucleotide

  bioRxiv (Cold Spring Harbor Laboratory) · 2024-11-15

  preprintOpen accessSenior authorCorresponding

  Abstract Intracellular membrane fusion is catalyzed by SNAREs, Rab GTPases, SM proteins, tethers, Sec18/NSF and Sec17/SNAP. Membrane fusion has been reconstituted with purified vacuolar proteins and lipids to address 3 salient questions: whether ATP hydrolysis by Sec18 affects its promotion of fusion, whether fusion promotion by Sec17 and Sec18 is only seen with mutant SNAREs or can also be seen with wild-type SNAREs, and whether Sec17 and Sec18 only promote fusion when they work together or whether they can each work separately. Fusion is driven by two engines, completion of SNARE zippering (which does not need Sec17/Sec18) and Sec17/Sec18-mediated fusion (needing SNAREs but not the energy from their complete zippering). Sec17 is required to rescue fusion that is blocked by incomplete zippering, though optimal rescue also needs the ATPase Sec18. ATP is an essential Sec18 ligand, but at limiting Sec17 levels Sec18 ATP hydrolysis also drives release of Sec17 without concomitant trans -SNARE complex disassembly. At higher (physiological) Sec17 levels, or without ATP hydrolysis, fusion prevails over Sec17 release. Stiff 16:0, 18:1 fatty acyl chain lipids provide an alternative route to suppressing fusion, with entirely wild-type SNAREs and without impediment to zippering. In this case, Sec17 and Sec18 restore comparable fusion with either ATP or a nonhydrolyzable analog. Fusion blocked by impaired zippering can be restored by concentrated Sec17 alone (but not by Sec18), while fusion inhibited by stiff fatty acyl chains is partially restored by Sec18 alone (but not by Sec17). With distinct fusion impediments, Sec18 and Sec17 have both shared roles and independent roles in promoting fusion. Significance Sec17/SNAP and Sec18/NSF catalyze cis -SNARE complex disassembly through ATP hydrolysis, but also drive fusion itself without ATP hydrolysis. Fusion can be inhibited by either “stiff” fatty acyl chains while allowing full zippering of entirely wild-type SNAREs or by incomplete SNARE zippering. In either case, Sec17 and Sec18 restore full fusion, but with clear differences. With defective zippering, high levels of Sec17 can restore fusion without Sec18. With stiff fatty acyl chains, Sec18 alone can restore fusion but Sec17 alone will not. In both cases, Sec17 and Sec18 are more efficient together. SNARE-dependent membrane fusion thus relies on two energy sources, complete SNARE zippering and interactions with Sec17 and Sec18.

  PublisherOA PDFDOI

• Sec18 binds the tethering/SM complex HOPS to engage the Qc-SNARE for membrane fusion

  Molecular Biology of the Cell · 2024-03-27 · 7 citations

  articleOpen accessSenior author

  Membrane fusion is regulated by Rab GTPases, their tethering effectors such as HOPS, SNARE proteins on each fusion partner, SM proteins to catalyze SNARE assembly, Sec17 (SNAP), and Sec18 (NSF). Though concentrated HOPS can support fusion without Sec18, we now report that fusion falls off sharply at lower HOPS levels, where direct Sec18 binding to HOPS restores fusion. This Sec18-dependent fusion needs adenine nucleotide but neither ATP hydrolysis nor Sec17. Sec18 enhances HOPS recognition of the Qc-SNARE. With high levels of HOPS, Qc has a Km for fusion of a few nM. Either lower HOPS levels, or substitution of a synthetic tether for HOPS, strikingly increases the Km for Qc to several hundred nM. With dilute HOPS, Sec18 returns the Km for Qc to low nM. In contrast, HOPS concentration and Sec18 have no effect on Qb-SNARE recognition. Just as Qc is required for fusion but not for the initial assembly of SNAREs in trans, impaired Qc recognition by limiting HOPS without Sec18 still allows substantial trans-SNARE assembly. Thus, in addition to the known Sec18 functions of disassembling SNARE complexes, oligomerizing Sec17 for membrane association, and allowing Sec17 to drive fusion without complete SNARE zippering, we report a fourth Sec18 function, the Sec17-independent binding of Sec18 to HOPS to enhance functional Qc-SNARE engagement.

  PublisherOA PDFDOI

Recent grants

• NIH Grant R01GM038895

  NIH · $2.5M · 2000

• NIH Grant R01GM023377

  NIH · $20.8M · 2017

• NIH Grant R37GM023377

  NIH · $5.2M · 1998

• INNER CENTROMERE TARGETING OF THE CHROMOSOME PASSENGER COMPLEX

  NIH · $10.6M · 2011–2016

• Mechanisms of Membrane Fusion

  NIH · $7.8M · 2016–2026

Frequent coauthors

• Christopher M. Hickey

  Arvinas (United States)

  33 shared

• Joji Mima

  Osaka University

  30 shared

• Christian Ungermann

  Osnabrück University

  26 shared

• Amy S. Burfeind

  Dartmouth College

  25 shared

• Nathan Margolis

  Dartmouth College

  20 shared

• Hongki Song

  Insmed (United States)

  17 shared

• Amy Orr

  Dartmouth College

  17 shared

• Albert Price

  15 shared