Evidence for a membrane-associated GTP-binding protein in Stigmatella aurantiaca, a prokaryotic cell

Translation initiation factor IF2 of the myxobacterium Stigmatella aurantiaca: presence of a single species with an unusual N-terminal sequence

The structural gene for translation initiation factor IF2 (infB) was isolated from the myxobacterium Stigmatella aurantiaca on a 5.18-kb BamHI genomic restriction fragment. The infB gene (ca. 3.16 kb) encodes a 1,054-residue polypeptide with extensive homology within its G domain and C terminus with the equivalent regions of IF2s from Escherichia coli, Bacillus subtilis, Bacillus stearothermophilus, and Streptococcus faecium. The N-terminal region does not display any significant homology to other known proteins. The S. aurantiaca infB gene encodes a single protein which cross-reacted with antiserum to E. coli IF2 and was able to complement an E. coli infB mutant. The S. aurantiaca IF2 is distinguished from all other IF2s by a sequence of 160 residues near the N terminus that has an unusual composition, made up essentially of alanine, proline, valine, and glutamic acid. Within this sequence, the pattern PXXXAP is repeated nine times. Complete deletion of this sequence did not affect the factor's function in initiation of translation and even increased its capacity to complement the E. coli infB mutant.

Neuropeptide Y promotes GTP photo-incorporation into a 55 kDa protein

Incubation of bovine hippocampal membranes with [alpha-32P]GTP and exposure to ultraviolet light resulted in the labelling of seven species with apparent molecular masses of 200, 74, 55, 53, 50, 43 and 40 kDa. Labelling of the 55 kDa species was greatly enhanced in the presence of carboxyl terminal fragments [neuropeptide Y-(18-36)] of neuropeptide Y. Labelling occurred with [alpha-32P]GTP but not [alpha-32P]ATP. A group of putative direct G protein activating peptides including mastoparan, melittin, substance P and adrenocorticotropic hormone (ACTH)-(1-24), were also able to stimulate the labelling of this protein. Labelling of the 55 kDa protein could be demonstrated in bovine brain but not peripheral tissues. Western blot analysis using an antibody against the common alpha subunit of G proteins recognized a protein co-migrating with the 55 kDa GTP-binding protein. These findings demonstrate the existence of a previously uncharacterized neuronal protein, with an apparent molecular mass of 55 kDa, that binds GTP in response to neuropeptide Y and other peptides.

Stimulation of inositide degradation in clumping Stigmatella aurantiaca

Numerous external signals which activate inositol phospholipid hydrolysis in eukaryotes are known; probably all of these signals are transduced by G proteins. So far, neither signal-transducing G protein nor receptor-regulated phospholipase C has been found in prokaryotes. However, a group of bacteria, the myxobacteria, displays cellular and tissue-like differentiation; therefore, it appeared that a search for the various activities involved in a signal-activated phosphatidylinositol cycle might be rewarding. Here, we report that in Stigmatella aurantiaca, under conditions which promote clumping, inositol phospholipid synthesis and degradation were stimulated with the resulting formation of inositol phosphate and inositol bisphosphate. The turnover was Ca2+ dependent and was increased by fluoride ions. Membrane preparations from these cells showed a phospholipase C activity which increased with the stage of incubation and which was stimulated by GTP gamma S, suggesting G protein dependency. To what extent this system in a prokaryotic cell shares properties of the phosphatidylinositol cycle in eukaryotes remains unexamined.

The possible role of ADP ribosylation in physiological regulation of sporulation in Streptomyces griseus

The role of ADP ribosylation of proteins in the physiological regulation of sporulation in Streptomyces griseus was studied. We report here that both the activity of NAD+: arginine ADP-ribosyltransferase (ADPRT) and the pattern of ADP-ribosylated proteins showed characteristic changes during the life cycle in S. griseus 2682. Analysis off ADP-ribosylated proteins revealed that in a nonsporulating mutant of the parental wild-type (wt) strain (Bld7 mutant), both the activity of ADPRT and the pattern of ADP-ribosylated proteins were different from those of the parental strain. Addition of 3-aminobenzamide (3AB), the most potent inhibitor of ADPRT, inhibited sporulation of S. griseus 2682 and the A-factor (AF)-induced sporulation of S. griseus Bld7, but in both cases the inhibitory effect of 3AB was strictly age-dependent. Using [alpha-32P]GTP, we have demonstrated the presence of GTP-binding proteins in purified cell membranes of S. griseus 2682 and S. griseus Bld7. The same GTP-binding proteins were observed in Bld7 and the wt. AF stimulated the basal GTPase activity of cell membranes of S. griseus 2682 in a concentration-dependent manner, suggesting that GTP-binding proteins might be involved in the AF-induced sporulation process.

Occurrence and biochemical characterization of GTP-binding proteins in Candida albicans

The activities of GTP-binding and GTPase in Candida albicans were present in the cytosol, KCl- and cholate-extractable fractions. At least two kinds of GTP-binding proteins were found in the cytosolic fraction; the major one with a molecular mass of about 30 kDa and the other about 500 kDa. The former specifically bound guanine nucleotides and was most likely to bind GDP since guanosine 5'-O-(thio) triphosphate (GTP gamma S)-binding was accelerated by addition of (NH4)2SO4. The latter showed no specificity in nucleotide binding and could also bind adenine nucleotides. The proteins were not ADP-ribosylated by either pertussis toxin or cholera toxin. These results indicate that ras-like monomeric, low molecular mass GTP-binding proteins distinct from heterotrimeric G proteins such as Gi, Go and Gs are present in C. albicans.

The identification of the Escherichia coli ftsY gene product: an unusual protein

The ftsYEX operon in Escherichia coli encodes three proteins, two of which (FtsE and FtsX) are known to be required for cell division. Although FtsE and FtsX have been identified using SDS-PAGE, the FtsY protein has not. We have used in vitro insertion mutagenesis to identify FtsY as a 92 kD polypeptide in maxicell experiments, although predictions from the DNA sequence estimated FtsY to be 54 kD. Results suggest that this disparity could be due to the unusually high percentage of acidic residues within the protein. Complementation tests indicated the presence of a promoter within ftsY required for expression of ftsE and ftsX. The FtsY protein exhibits sequence homology with the SR alpha protein of eukaryotes which is involved in protein secretion. The essential nature of the ftsY gene was also demonstrated.

Protein kinase activities in cell-free extracts of Streptomyces coelicolor A3(2)

Protein kinase activities were detected in cell-free extracts of the B385 derivative of Streptomyces coelicolor A3(2); at least 12 polypeptides, ranging in Mr from 6,000 to 98,000, were detectably phosphorylated, probably as O-monoesters, after incubation with gamma [32P]ATP. The culture stage of the mycelia used for production of the cell-free extracts determined the profile of phosphorylated polypeptides. Phosphoenol pyruvate acted as a potent modulator of the apparent degree of protein kinase activity. In addition Ca2+ ions, verapamil, chlorpromazine and anti-calmodulin antiserum had specific effects on the profile of phosphopolypeptides observed.