Proposal for new catalytic roles for two invariant residues in Escherichia coli ribonuclease HI.

Three mutants of Escherichia coli ribonuclease HI, in which an invariant acidic residue Asp134 was replaced, were crystallized, and their three-dimensional structures were determined by X-ray crystallography. The D134A mutant is completely inactive, whereas the other two mutants, D134H and D134N, retain 59 and 90% activities relative to the wild-type, respectively. The overall structures of these three mutant proteins are identical with that of the wild-type enzyme, except for local conformational changes of the flexible loops.

Membrane topology and site-specific mutagenesis of Pseudomonas aeruginosa porin OprD.

Pseudomonas aeruginosa OprD is a 420-amino-acid protein that facilitates the uptake of basic amino acids, imipenem and gluconate across the outer membrane. OprD was the first specific porin that could be aligned with members of the non-specific porin super-family. Utilizing multiple alignments in conjugation with structure predictions and amphipathicity calculations, an OprD-topology model was proposed.

Structural and functional alterations of a colicin-resistant mutant of OmpF porin from Escherichia coli.

A strain of Escherichia coli, selected on the basis of its resistance to colicin N, reveals distinct structural and functional alterations in unspecific OmpF porin. A single mutation [Gly-119-->Asp (G119D)] was identified in the internal loop L3 that contributes critically to the formation of the construction inside the lumen of the pore. X-ray structure analysis to a resolution of 3.

Diversity of the P2 protein among nontypeable Haemophilus influenzae isolates.

The genes for outer membrane protein P2 of four nontypeable Haemophilus influenzae strains were cloned and sequenced. The derived amino acid sequences were compared with the outer membrane protein P2 sequence from H. influenzae type b MinnA and the sequences of P2 from three additional nontypeable H.

Membrane-bound form of the pore-forming domain of colicin A. A neutron scattering study.

The ion-channel forming C-terminal fragment of colicin A binds to negatively charged lipid vesicles and provides an example of the insertion of a soluble protein into a lipid bilayer. The soluble structure is known and consists of a ten-helix bundle containing a hydrophobic helical hairpin. This fragment forms a well-defined complex with dimyristoylphosphatidyl-glycerol which is thus amenable to neutron scattering studies.

Purification of Aeromonas hydrophila major outer-membrane proteins: N-terminal sequence analysis and channel-forming properties.

Four outer-membrane proteins of Aeromonas hydrophila were purified and their N-terminal sequences and channel-forming properties were determined. Three could be matched with proteins from other species. One was a maltoporin, as its level increased when cells were grown in maltose-containing media, and the channel it formed was blocked by maltose.

The bacterial porin superfamily: sequence alignment and structure prediction.

The porins of Gram-negative bacteria are responsible for the 'molecular sieve' properties of the outer membrane. They form large water-filled channels which allow the diffusion of hydrophilic molecules into the periplasmic space. Owing to the strong hydrophilicity of their amino acid sequence and the nature of their secondary structure (beta strands), conventional hydropathy methods for predicting membrane topology are useless for this class of protein.