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SUMMARY:Linking mechanochemistry with protein folding with single bond res
 olution - Prof. Sergi Garcia-Manyes\, Department of Physics and and Randal
 l Division of Cell and Molecular Biophysics\, King's College London 
DTSTART:20180504T150000Z
DTEND:20180504T160000Z
UID:TALK87141@talks.cam.ac.uk
CONTACT:Lorenzo Di Michele
DESCRIPTION:The nanomechanical properties of elastomeric proteins determin
 e the elasticity of a variety of tissues. Post-translational modifications
  (PTMs) have recently emerged as a useful tactic to regulate protein nanom
 echanics. In particular\, the presence of covalent disulfide bonds\, argua
 bly the most relevant PTM with a significant mechanical role\, is a widesp
 read natural strategy to regulate protein extensibility and enhance protei
 n stiffness. The prevalent in-vivo strategy to form disulfide bonds requir
 es the presence of dedicated enzymes. Here we propose two alternative chem
 ical routes to promote non-enzymatic oxidative protein folding through the
  reactivity of protein based chemical modifications. Using single-molecule
  force-clamp spectroscopy and mass spectrometry\, we first captured the re
 activity of an individual sulfenic acid\, a PTM that functions as a key se
 nsor of oxidative stress\, when embedded within the core of a single Ig do
 main of the titin protein. Our results demonstrated that sulfenic acid is 
 a crucial short-lived intermediate that dictates the protein’s fate in a
  conformation-dependent manner. When exposed to the solution\, sulfenic ac
 id rapidly undergoes further chemical modification\, leading to irreversib
 le protein misfolding\; when cryptic in the protein’s microenvironment\,
  it readily condenses with a neighbouring thiol to create a protective dis
 ulfide bond\, which assists the functional folding of the protein. A secon
 d\, alternative method to induce disulfide reformation occurs via disulfid
 e isomerization of naturally occurring small thiols. Our single molecule a
 pproach\, complemented with DFT calculations revealed that subtle changes 
 in the chemical structure of a transient mixed-disulfide intermediate addu
 ct between a protein cysteine and an attacking low molecular-weight thiol 
 have a dramatic effect on the protein’s mechanical stability. Combined\,
  these chemistry-based mechanisms for non-enzymatic oxidative folding prov
 ide a plausible explanation for redox-modulated stiffness of proteins that
  are physiologically exposed to mechanical forces\, such as cardiac titin.
LOCATION:Small Lecture Theatre\, Cavendish Laboratory
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