Helen R Saibil

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Arthur L. Horwich49
Susan L Lindquist40
Wah Chiu40
David N Mastronarde40
Thomas E. Ferrin37
38Elena V. Orlova
38Robert J. C. Gilbert
32Daniel K. Clare
32Wah Chiu
31Christopher M. Dobson

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1976
2017
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Hsp26: a temperature-regulated chaperone.
Small heat shock proteins (sHsps) are a conserved protein family, with members found in all organisms analysed so far. Several sHsps have been shown to exhibit chaperone activity and protect proteins from irreversible aggregation in vitro. Here we show that Hsp26, an sHsp from Saccharomyces cerevisiae, is a temperature-regulated molecular chaperone. Like… (More)
A small heat shock protein stably binds heat-denatured model substrates and can maintain a substrate in a folding-competent state.
The small heat shock proteins (sHSPs) recently have been reported to have molecular chaperone activity in vitro; however, the mechanism of this activity is poorly defined. We found that HSP18.1, a dodecameric sHSP from pea, prevented the aggregation of malate dehydrogenase (MDH) and glyceraldehyde-3-phosphate dehydrogenase heated to 45 degrees C. Under… (More)
Structural Basis of Pore Formation by the Bacterial Toxin Pneumolysin
The bacterial toxin pneumolysin is released as a soluble monomer that kills target cells by assembling into large oligomeric rings and forming pores in cholesterol-containing membranes. Using cryo-EM and image processing, we have determined the structures of membrane-surface bound (prepore) and inserted-pore oligomer forms, providing a direct observation of… (More)
Reversible conversion of monomeric human prion protein between native and fibrilogenic conformations.
Prion propagation involves the conversion of cellular prion protein (PrPC) into a disease-specific isomer, PrPSc, shifting from a predominantly alpha-helical to beta-sheet structure. Here, conditions were established in which recombinant human PrP could switch between the native alpha conformation, characteristic of PrPC, and a compact, highly soluble,… (More)
The TatA component of the twin-arginine protein transport system forms channel complexes of variable diameter.
The Tat system mediates Sec-independent transport of folded precursor proteins across the bacterial plasma membrane or the chloroplast thylakoid membrane. Tat transport involves distinct high-molecular-weight TatA and TatBC complexes. Here we report the 3D architecture of the TatA complex from Escherichia coli obtained by single-particle electron microscopy… (More)
Secretin PulD: association with pilot PulS, structure, and ion-conducting channel formation.
The outer membrane protein PulD (secretin) of Klebsiella oxytoca is required for transport of pullulanase across this membrane. We have purified a multimeric PulD complex from an Escherichia coli strain expressing all the proteins involved in pullulanase secretion. The outer membrane-anchored lipoprotein PulS was found to copurify with PulD. The molar ratio… (More)
GroEL-GroES Cycling ATP and Nonnative Polypeptide Direct Alternation of Folding-Active Rings
The double-ring chaperonin GroEL mediates protein folding in the central cavity of a ring bound by ATP and GroES, but it is unclear how GroEL cycles from one folding-active complex to the next. We observe that hydrolysis of ATP within the cis ring must occur before either nonnative polypeptide or GroES can bind to the trans ring, and this is associated with… (More)
Detection and separation of heterogeneity in molecular complexes by statistical analysis of their two-dimensional projections.
Progress in molecular structure determination by cryo electron microscopy and single particle analysis has led to improvements in the resolution achievable. However, in many cases the limiting factor is structural heterogeneity of the sample. To address this problem, we have developed a method based on statistical analysis of the two-dimensional images to… (More)
Two Structural Transitions in Membrane Pore Formation by Pneumolysin, the Pore-Forming Toxin of Streptococcus pneumoniae
The human pathogen Streptococcus pneumoniae produces soluble pneumolysin monomers that bind host cell membranes to form ring-shaped, oligomeric pores. We have determined three-dimensional structures of a helical oligomer of pneumolysin and of a membrane-bound ring form by cryo-electron microscopy. Fitting the four domains from the crystal structure of the… (More)
Mechanism of GroEL action: Productive release of polypeptide from a sequestered position under groes
The chaperonin GroEL is a large, double-ring structure that, together with ATP and the cochaperonin GroES, assists protein folding in vivo. GroES forms an asymmetric complex with GroEL in which a single GroES ring binds one end of the GroEL cylinder. Cross-linking studies reveal that polypeptide binding occurs exclusively to the GroEL ring not occupied by… (More)