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Biomedical subjects

C Finnie

Publications and source records attributed to C Finnie.

4 recordsLinked to original sources
PubMed2000

Extracellular glycanases of Rhizobium leguminosarum are activated on the cell surface by an exopolysaccharide-related component.

Rhizobium leguminosarum secretes two extracellular glycanases, PlyA and PlyB, that can degrade exopolysaccharide (EPS) and carboxymethyl cellulose (CMC), which is used as a model substrate of plant cell wall cellulose polymers. When grown on agar medium, CMC degradation occurred only directly below colonies of R. leguminosarum, suggesting that the enzymes remain attached to the bacteria. Unexpectedly, when a PlyA-PlyB-secreting colony was grown in close proximity to mutants unable to produce or secrete PlyA and PlyB, CMC degradation occurred below that part of the mutant colonies closest to the wild type. There was no CMC degradation in the region between the colonies. By growing PlyB-secreting colonies on a lawn of CMC-nondegrading mutants, we could observe a halo of CMC degradation around the colony. Using various mutant strains, we demonstrate that PlyB diffuses beyond the edge of the colony but does not degrade CMC unless it is in contact with the appropriate colony surface. PlyA appears to remain attached to the cells since no such diffusion of PlyA activity was observed. EPS defective mutants could secrete both PlyA and PlyB, but these enzymes were inactive unless they came into contact with an EPS(+) strain, indicating that EPS is required for activation of PlyA and PlyB. However, we were unable to activate CMC degradation with a crude EPS fraction, indicating that activation of CMC degradation may require an intermediate in EPS biosynthesis. Transfer of PlyB to Agrobacterium tumefaciens enabled it to degrade CMC, but this was only observed if it was grown on a lawn of R. leguminosarum. This indicates that the surface of A. tumefaciens is inappropriate to activate CMC degradation by PlyB. Analysis of CMC degradation by other rhizobia suggests that activation of secreted glycanases by surface components may occur in other species.

Carboxymethylcellulose Sodium↗
PubMed1999

14-3-3 proteins: eukaryotic regulatory proteins with many functions.

The enigmatically named 14-3-3 proteins have been the subject of considerable attention in recent years since they have been implicated in the regulation of diverse physiological processes, in eukaryotes ranging from slime moulds to higher plants. In plants they have roles in the regulation of the plasma membrane H+-ATPase and nitrate reductase, among others. Regulation of target proteins is achieved through binding of 14-3-3 to short, often phosphorylated motifs in the target, resulting either in its activation (e.g. H+-ATPase), inactivation (e.g. nitrate reductase) or translocation (although this function of 14-3-3 proteins has yet to be demonstrated in plants). The native 14-3-3 proteins are homo- or heterodimers and, as each monomer has a binding site, a dimer can potentially bind two targets, promoting their association. Alternatively, target proteins may have more than one 14-3-3-binding site. In this mini review, we present a synthesis of recent results from plant 14-3-3 research and, with reference to known 14-3-3-binding motifs, suggest further subjects for research.

14-3-3 Proteins↗
PubMed1998

Characterization of Rhizobium leguminosarum exopolysaccharide glycanases that are secreted via a type I exporter and have a novel heptapeptide repeat motif.

The prsDE genes encode a type I protein secretion system required for the secretion of the nodulation protein NodO and at least three other proteins from Rhizobium leguminosarum bv. viciae. At least one of these proteins was predicted to be a glycanase involved in processing of bacterial exopolysaccharide (EPS). Two strongly homologous genes (plyA and plyB) were identified as encoding secreted proteins with polysaccharide degradation activity. Both PlyA and PlyB degrade EPS and carboxymethyl cellulose (CMC), and these extracellular activities are absent in a prsD (protein secretion) mutant. The plyA gene is upstream of prsD but appears to be expressed at a very low level (if at all) in cultured bacteria. A plyB::Tn5 mutant has a very large reduction in degradation of EPS and CMC. Cultures of plyB mutants contained an increased ratio of EPS repeat units to reducing ends, indicating that the EPS was present in a longer-chain form, and this correlated with a significant increase in culture viscosity. Thus, PlyB may play a role in processing of EPS. Analysis of the symbiotic properties of a plyA plyB double mutant revealed that these genes are not required for symbiotic nitrogen fixation and that nodulation was not significantly affected. PlyA and PlyB are similar to bacterial and fungal polysaccharide lyases; they contain 10 copies of what we propose as a novel heptapeptide repeat motif that may constitute a fold similar to that found in the family of extracellular pectate lyases. PlyA and PlyB lack the Ca2+-binding RTX nonapeptide repeat motifs usually found in proteins secreted via type I systems. We propose that PlyA and PlyB are members of a new family of proteins secreted via type I secretion systems and that they are involved in processing of EPS.

Amino Acid Sequence↗