Biomedical subjects

Maria Silow

Publications and source records attributed to Maria Silow.

3 recordsLinked to original sources

PubMed2003

High concentrations of viscogens decrease the protein folding rate constant by prematurely collapsing the coil.

In several studies, viscogenic osmolytes have been suggested to decrease the folding rate constant of polypeptides by slowing their motion through the solvent. Here, we show that osmolytes may slow protein folding by prematurely collapsing the coil. At low or moderate concentrations of osmolytes (<30%), folding of the two-state protein CI2 becomes faster with increasing osmolyte concentrations, suggesting that the kinetics are governed by protein stability. However, at higher concentrations of osmolyte, the coil collapses in the dead-time of the refolding experiment, causing a dramatic drop in the folding rate. The collapsed state is non-native and appears to be different for different osmolytes.

Ethylene Glycol↗

PubMed2002

Functional role of internal water molecules in rhodopsin revealed by X-ray crystallography.

Activation of G protein-coupled receptors (GPCRs) is triggered and regulated by structural rearrangement of the transmembrane heptahelical bundle containing a number of highly conserved residues. In rhodopsin, a prototypical GPCR, the helical bundle accommodates an intrinsic inverse-agonist 11-cis-retinal, which undergoes photo-isomerization to the all-trans form upon light absorption. Such a trigger by the chromophore corresponds to binding of a diffusible ligand to other GPCRs. Here we have explored the functional role of water molecules in the transmembrane region of bovine rhodopsin by using x-ray diffraction to 2.6 A. The structural model suggests that water molecules, which were observed in the vicinity of highly conserved residues and in the retinal pocket, regulate the activity of rhodopsin-like GPCRs and spectral tuning in visual pigments, respectively. To confirm the physiological relevance of the structural findings, we conducted single-crystal microspectrophotometry on rhodopsin packed in our three-dimensional crystals and show that its spectroscopic properties are similar to those previously found by using bovine rhodopsin in suspension or membrane environment.

Animals↗

PubMed2002

A peptide methionine sulfoxide reductase highly expressed in photosynthetic tissue in Arabidopsis thaliana can protect the chaperone-like activity of a chloroplast-localized small heat shock protein.

The oxidation of methionine residues in proteins to methionine sulfoxides occurs frequently and protein repair by reduction of the methionine sulfoxides is mediated by an enzyme, peptide methionine sulfoxide reductase (PMSR, EC 1.8.4.6), universally present in the genomes of all so far sequenced organisms. Recently, five PMSR-like genes were identified in Arabidopsis thaliana, including one plastidic isoform, chloroplast localised plastidial peptide methionine sulfoxide reductase (pPMSR) that was chloroplast-localized and highly expressed in actively photosynthesizing tissue (Sadanandom A et al., 2000). However, no endogenous substrate to the pPMSR was identified. Here we report that a set of highly conserved methionine residues in Hsp21, a chloroplast-localized small heat shock protein, can become sulfoxidized and thereafter reduced back to methionines by this pPMSR. The pPMSR activity was evaluated using recombinantly expressed pPMSR and Hsp21 from Arabidopsis thaliana and a direct detection of methionine sulfoxides in Hsp21 by mass spectrometry. The pPMSR-catalyzed reduction of Hsp21 methionine sulfoxides occurred on a minute time-scale, was ultimately DTT-dependent and led to recovery of Hsp21 conformation and chaperone-like activity, both of which are lost upon methionine sulfoxidation (Härndahl et al., 2001). These data indicate that one important function of pPMSR may be to prevent inactivation of Hsp21 by methionine sulfoxidation, since small heat shock proteins are crucial for cellular resistance to oxidative stress.

Arabidopsis↗