Vladimir A. Meshcheryakov

Inhibition of a type III secretion system by the deletion of a short loop in one of its membrane proteins

Crystal structures of the cytoplasmic domain of FlhB from S. typhimurium and A. aeolicus were solved at 2.45 and 2.55 Å resolution, respectively. The deletion of a short loop in the cytoplasmic domain of Salmonella FlhB completely abolishes secretion by the type III secretion system. A molecular-dynamics simulation shows that the deletion of the loop affects the flexibility of a linker between the transmembrane and cytoplasmic domains of FlhB.

Crystal structure of the flagellar accessory protein FlaH of Methanocaldococcus jannaschii suggests a regulatory role in archaeal flagellum assembly.

Archaeal flagella are unique structures that share functional similarity with bacterial flagella, but are structurally related to bacterial type IV pili. The flagellar accessory protein FlaH is one of the conserved components of the archaeal motility system. However, its function is not clearly understood. Here, we present the 2.2 Å resolution crystal structure of FlaH from the hyperthermophilic archaeon, Methanocaldococcus jannaschii. The protein has a characteristic RecA‐like fold, which has been found previously both in archaea and bacteria. We show that FlaH binds to immobilized ATP—however, it lacks ATPase activity. Surface plasmon resonance analysis demonstrates that ATP affects the interaction between FlaH and the archaeal motor protein FlaI. In the presence of ATP, the FlaH‐FlaI interaction becomes significantly weaker. A database search revealed similarity between FlaH and several DNA‐binding proteins of the RecA superfamily. The closest structural homologs of FlaH are KaiC‐like proteins, which are archaeal homologs of the circadian clock protein KaiC from cyanobacteria. We propose that one of the functions of FlaH may be the regulation of archaeal motor complex assembly.

Function of FlhB, a Membrane Protein Implicated in the Bacterial Flagellar Type III Secretion System

The membrane protein FlhB is a highly conserved component of the flagellar secretion system, and it plays an active role in the regulation of protein export. In this study conserved properties of FlhB that are important for its function were investigated. Replacing the flhB gene (or part of the gene) in Salmonella typhimurium with the flhB gene of the distantly related bacterium Aquifex aeolicus greatly reduces motility. However, motility can be restored to some extent by spontaneous mutations in the part of flhB gene coding for the cytoplasmic domain of Aquifex FlhB. Structural analysis suggests that these mutations destabilize the structure. The secondary structure and stability of the mutated cytoplasmic fragments of FlhB have been studied by circular dichroism spectroscopy. The results suggest that conformational flexibility could be important for FlhB function. An extragenic suppressor mutation in the fliS gene, which decreases the affinity of FliS to FliC, partially restores motility of the FlhB substitution mutants.

Structure of a tropomyosin N-terminal fragment at 0.98 Å resolution

Tropomyosin (TM) is an elongated two-chain protein that binds along actin filaments. Important binding sites are localized in the N-terminus of tropomyosin. The structure of the N-terminus of the long muscle α-TM has been solved by both NMR and X-ray crystallography. Only the NMR structure of the N-terminus of the short nonmuscle α-TM is available. Here, the crystal structure of the N-terminus of the short nonmuscle α-TM (αTm1bZip) at a resolution of 0.98 Å is reported, which was solved from crystals belonging to space group P3(1) with unit-cell parameters a = b = 33.00, c = 52.03 Å, α = β = 90, γ = 120°. The first five N-terminal residues are flexible and residues 6-35 form an α-helical coiled coil. The overall fold and the secondary structure of the crystal structure of αTM1bZip are highly similar to the NMR structure and the atomic coordinates of the corresponding C(α) atoms between the two structures superimpose with a root-mean-square deviation of 0.60 Å. The crystal structure validates the NMR structure, with the positions of the side chains being determined precisely in our structure.

Purification, crystallization and preliminary X-ray crystallographic analysis of the C-terminal cytoplasmic domain of FlhB from Aquifex aeolicus

FlhB is a key protein in the regulation of protein export by the bacterial flagellar secretion system. It is composed of two domains: an N-terminal transmembrane domain and a C-terminal cytoplasmic domain (FlhBc). Here, the crystallization and preliminary crystallographic analysis of FlhBc from Aquifex aeolicus are reported. Purified protein was crystallized using the vapour-diffusion technique. The crystals diffracted to 2.3 Å resolution and belonged to space group C2, with unit-cell parameters a = 114.49, b = 33.89, c = 122.13 Å, β = 107.53°.

Purification, crystallization and preliminary X-ray crystallographic analysis of the C-terminal cytoplasmic domain of FlhB from Salmonella typhimurium

FlhB is a key protein in the regulation of protein export by the bacterial flagellar secretion system. It is composed of two domains: an N-terminal transmembrane domain and a C-terminal cytoplasmic domain (FlhBc). FlhBc from Salmonella typhimurium has been successfully crystallized using the vapour-diffusion method. The crystals diffracted to 2.45 Å resolution and belonged to space group P4(2)2(1)2, with unit-cell parameters a=b=49.06, c=142.94 Å. A selenomethionine-containing variant of FlhBc has also been crystallized in the same space group and was used for initial phase calculation by the multiwavelength anomalous dispersion (MAD) method.

Crystallization and preliminary X-ray crystallographic analysis of full-length yeast tropomyosin 2 from Saccharomyces cerevisiae.

Tropomyosin is a highly conserved actin-binding protein that is found in most eukaryotic cells. It is critical for actin-filament stabilization and for cooperative regulation of many actin functions. Detailed structural information on tropomyosin is very important in order to understand the mechanisms of its action. Whereas structures of isolated tropomyosin fragments have been obtained at high resolution, the atomic structure of the entire tropomyosin molecule is still unknown. Here, the crystallization and preliminary crystallographic analysis of full-length yeast tropomyosin 2 (yTm2) from Saccharomyces cerevisiae are reported. Recombinant yTm2 expressed in Escherichia coli was crystallized using the hanging-drop vapour-diffusion method. The crystals belonged to space group C2, with unit-cell parameters a = 154.8, b = 49.9, c = 104.0 A, alpha = gamma = 90.0, beta = 124.0 degrees and two molecules in the asymmetric unit. A complete native X-ray diffraction data set was collected to 3.5 A resolution using synchrotron radiation.

Purification, crystallization and preliminary X-ray crystallographic analysis of the flagellar accessory protein FlaH from the methanogenic archaeon Methanocaldococcus jannaschii

The flagellar accessory protein FlaH is thought to be one of the essential components of an archaeal motility system. However, to date biochemical and structural information about this protein has been limited. Here, the crystallization of FlaH from the hyperthermophilic archaeon Methanocaldococcus jannaschii is reported. Protein crystals were obtained by the vapour-diffusion method. These crystals belonged to space group P3₁21, with unit-cell parameters a=b=131.42, c=89.35 Å. The initial solution of the FlaH structure has been determined by multiple-wavelength anomalous dispersion phasing using a selenomethionine-derivatized crystal.

Structural flexibility of the periplasmic protein, FlgA, regulates flagellar P-ring assembly in Salmonella enterica

A periplasmic flagellar chaperone protein, FlgA, is required for P-ring assembly in bacterial flagella of taxa such as Salmonella enterica or Escherichia coli. The mechanism of chaperone-mediated P-ring formation is poorly understood. Here we present the open and closed crystal structures of FlgA from Salmonella enterica serovar Typhimurium, grown under different crystallization conditions. An intramolecular disulfide cross-linked form of FlgA caused a dominant negative effect on motility of the wild-type strain. Pull-down experiments support a specific protein-protein interaction between FlgI, the P-ring component protein, and the C-terminal domain of FlgA. Surface plasmon resonance and limited-proteolysis indicate that flexibility of the domain is reduced in the covalently closed form. These results show that the structural flexibility of the C-terminal domain of FlgA, which is related to the structural difference between the two crystal forms, is intrinsically associated with its molecular chaperone function in P-ring assembly.