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Nicholas M Glykos

Publications and source records attributed to Nicholas M Glykos.

7 recordsLinked to original sources
PubMed2006

Software news and updates. Carma: a molecular dynamics analysis program.

A computer program has been developed to aid the analysis of molecular dynamics trajectories. The program is tuned for macromolecular large-scale problems and supports features such as removal of global translations-rotations of the solute, calculation of average distance maps and their corresponding standard deviations, calculation of the variance-covariance and cross-correlation matrices, and principal component analysis of trajectories with the added ability to create artificial trajectories based on selected eigenvectors. Limited graphics (trajectory viewing) capabilities are also available.

Computer Simulation↗
PubMed2006

Loopless Rop: structure and dynamics of an engineered homotetrameric variant of the repressor of primer protein.

The repressor of primer (Rop) protein has become a steady source of surprises concerning the relationship between the sequences and the structures of several of its mutants and variants. Here we add another piece to the puzzle of Rop by showing that an engineered deletion mutant of the protein (corresponding to a deletion of residues 30-34 of the wild-type protein and designed to restore the heptad periodicity at the turn region) results in a complete reorganization of the bundle which is converted from a homodimer to a homotetramer. In contrast (and as previously shown), a two-residue insertion, which also restores the heptad periodicity, is essentially identical with wild-type Rop. The new deletion mutant structure is a canonical, left-handed, all-antiparallel bundle with a completely different hydrophobic core and distinct surface properties. The structure agrees and qualitatively explains the results from functional, thermodynamic, and kinetic studies which indicated that this deletion mutant is a biologically inactive hyperstable homotetramer. Additional insight into the stability and dynamics of the mutant structure has been obtained from extensive molecular dynamics simulations in explicit water and with full treatment of electrostatics.

Amino Acid Sequence↗
PubMed2004

Ionic strength reducers: an efficient approach to protein purification and crystallization. Application to two Rop variants.

Detailed knowledge of the influence of various parameters on macromolecular solubility is essential for crystallization. The concept of so-called 'ionic strength reducers' provides insight into the changes in solubility induced by organic solvents and hydrophilic polymers in aqueous electrolytic solutions. A simple and efficient procedure is presented which exploits the properties of ionic strength reducers in the purification and crystallization of proteins. Using two designed variants of the Rop protein as model systems, superior crystals have been obtained compared with conventional techniques. This procedure is particularly useful in cases where excessive nucleation leads to the growth of a large number of tiny crystals that are useless for crystallographic analysis.

Alanine↗
PubMed2003

Structure of HrcQB-C, a conserved component of the bacterial type III secretion systems.

Type III secretion systems enable plant and animal bacterial pathogens to deliver virulence proteins into the cytosol of eukaryotic host cells, causing a broad spectrum of diseases including bacteremia, septicemia, typhoid fever, and bubonic plague in mammals, and localized lesions, systemic wilting, and blights in plants. In addition, type III secretion systems are also required for biogenesis of the bacterial flagellum. The HrcQ(B) protein, a component of the secretion apparatus of Pseudomonas syringae with homologues in all type III systems, has a variable N-terminal and a conserved C-terminal domain (HrcQ(B)-C). Here, we report the crystal structure of HrcQ(B)-C and show that this domain retains the ability of the full-length protein to interact with other type III components. A 3D analysis of sequence conservation patterns reveals two clusters of residues potentially involved in protein-protein interactions. Based on the analogies between HrcQ(B) and its flagellum homologues, we propose that HrcQ(B)-C participates in the formation of a C-ring-like assembly.

Amino Acid Sequence↗
PubMed2003

Structure determination of a small protein through a 23-dimensional molecular-replacement search.

The crystal structure of a 4-alpha-helical bundle protein has been determined by the application of a 23-dimensional molecular-replacement search performed using a stochastic method. The search model for the calculation was a 26-residue-long polyalanine helix amounting to less than 13% of the total number of atoms in the asymmetric unit of the target crystal structure. The crystal structure determination procedure is presented in detail, with emphasis on the molecular-replacement calculations.

Bacterial Proteins↗
PubMed2002

The structure of AhrC, the arginine repressor/activator protein from Bacillus subtilis.

In the Gram-positive bacterium Bacillus subtilis the concentration of the amino acid L-arginine is controlled by the transcriptional regulator AhrC. The hexameric AhrC protein binds in an L-arginine-dependent manner to pseudo-palindromic operators within the promoter regions of arginine biosynthetic and catabolic gene clusters. AhrC binding results in the repression of transcription of biosynthetic genes and in the activation of transcription of catabolic genes. The crystal structure of AhrC has been determined at 2.7 A resolution. Each subunit of the protein has two domains. The C-terminal domains are arranged with 32 point-group symmetry and mediate the major intersubunit interactions. The N-terminal domains are located around this core, where they lie in weakly associated pairs but do not obey strict symmetry. A structural comparison of AhrC with the arginine repressor from the thermophile B. stearothermophilus reveals close similarity in regions implicated in L-arginine binding and DNA recognition, but also reveals some striking sequence differences, especially within the C-terminal oligomerization domain, which may contribute to the different thermostabilities of the proteins. Comparison of the crystal structure of AhrC with a 30 A resolution model obtained by combining X-ray structure-factor amplitudes with phases derived from electron-microscopic analyses of AhrC crystals confirms the essential accuracy of the earlier model and suggests that such an approach may be more widely useful for obtaining low-resolution phase information.

Amino Acid Sequence↗