Distinct cysteine sulfhydryl environments detected by analysis of Raman S-hh markers of Cys-->Ser mutant proteins

Trapping of arsenite by mercaptopropyl-functionalized mesostructured silica with a wormhole framework

Thiol-functionalized mesostructured silica, prepared by direct assembly methods, is an effective trapping agent for the removal of arsenite from water.

Construction and characterization of a kappa opioid receptor devoid of all free cysteines

We have constructed an optimized mutant of the kappa opioid receptor (KOR), which is devoid of its 10 free cysteines. It was necessary to test different amino acid replacements at various positions and we used a structural model and homology with other receptor family members as a guide. This mutant binds ligands and couples to the cognate G-proteins in a very similar fashion to wild-type KOR. The addition of the antagonist naloxone during cell growth greatly enhances heterogeneous expression of the mutant in mammalian cells, such that amounts similar to wild-type could be produced. We showed by fluorescence microscopy that naloxone stabilizes the mutant in the plasma membrane. This mutant, which now permits the insertion of single cysteines, was designed for use in spectroscopic studies of ligand-induced receptor conformational changes as well as to simplify folding studies.

Nonnative interactions between cysteines direct productive assembly of P22 tailspike protein

Nonnative disulfide bond formation can play a critical role in the assembly of disulfide bonded proteins. During the folding and assembly of the P22 tailspike protein, nonnative disulfide bonds form both in vivo and in vitro. However, the mechanism and identity of cysteine disulfide pairs remains elusive, particularly for P22 tailspike, which contains no disulfide bonds in its native, functional form. Understanding the interactions between cysteine residues is important for developing a mechanistic model for the role of nonnative cysteines in P22 tailspike assembly. Prior in vivo studies have suggested that cysteines 496, 613, and 635 are the most likely site for sulfhydryl reactivity. Here we demonstrate that these three cysteines are critical for efficient assembly of tailspike trimers, and that interactions between cysteine pairs lead to productive assembly of native tailspike.

New structural insights from Raman spectroscopy of proteins and their assemblies

Protein structure and stability are sensitive to and dependent on the local interactions of amino acid side chains. A diverse and important type of side-chain interaction is the hydrogen bond. Although numerous hydrogen bonds are resolved in protein 3-dimensional structures, those of the cysteine sulfhydryl group (S-H) are elusive to high-resolution X-ray and NMR methods. However, the nature and strength of sulfhydryl hydrogen bonds (S-H* * *X) are amenable to investigation by Raman spectroscopy. The power of the Raman method for characterizing S-H* * *X interactions is illustrated by resolving the Raman S-H stretching band for each of the eight cysteines per 666-residue subunit in the trimeric tailspike of icosahedral bacteriophage P22. The Raman sulfhydryl signatures of the wild-type tailspike and eight single-site cysteine to serine mutants reveal a heretofore unrecognized diversity of S-H hydrogen bonds in a native protein. The use of Raman spectroscopy to identify the non-hydrogen-bonded state of the tyrosine phenoxyl group is also described. This unusual and unexpected state occurs for all tyrosines in the assembled capsids of filamentous viruses Ff and Pf1. The Raman spectral signature of the non-hydrogen-bonded tyrosine phenoxyl, which is characterized by an extraordinary Raman Fermi doublet intensity ratio (I850/I830 = 6.7), extends and refines the existing correlation for hydrogen-bonded tyrosines. Finally, a novel Raman signature for tryptophan in the Pf3 filamentous virus is identified, which is proposed as diagnostic of "cation-pi interaction" involving the guanidinium group of Arg 37 as a cation donor and the indolyl ring of Trp 38 as a pi-electron acceptor. These studies demonstrate the power of Raman spectroscopy for investigating the interactions of key side chains in native protein assemblies.

The interdigitated beta-helix domain of the P22 tailspike protein acts as a molecular clamp in trimer stabilization

The P22 tailspike adhesin is an elongated thermostable trimer resistant to protease digestion and to denaturation in sodium dodecyl sulfate. Monomeric, dimeric, and protrimeric folding and assembly intermediates lack this stability and are thermolabile. In the native trimer, three right-handed parallel beta-helices (residues 143-540), pack side-by-side around the three-fold axis. After residue 540, these single chain beta-helices terminate and residues 541-567 of the three polypeptide chains wrap around each other to form a three-stranded interdigitated beta-helix. Three mutants located in this region -- G546D, R563Q, and A575T -- blocked formation of native tailspike trimers, and accumulated soluble forms of the mutant polypeptide chains within cells. The substitutions R563Q and A575T appeared to prevent stable association of partially folded monomers. G546D, in the interdigitated region of the chain, blocked tailspike folding at the transition from the partially-folded protrimer to the native trimer. The protrimer-like species accumulating in the G546D mutant melted out at 42 degrees C and was trypsin and SDS sensitive. The G546D defect was not corrected by introduction of global suppressor mutations, which correct kinetic defects in beta-helix folding. The simplest interpretation of these results is that the very high thermostability (T(m) = 88 degrees C), protease and detergent resistance of the native tailspike acquired in the protrimer-to-trimer transition, depends on the formation of the three-stranded interdigitated region. This interdigitated beta-helix appears to function as a molecular clamp insuring thermostable subunit association in the native trimer.