Biomedical subjects

A A Rodal

Publications and source records attributed to A A Rodal.

6 recordsLinked to original sources

PubMed2001

Activation of the Arp2/3 complex by the actin filament binding protein Abp1p.

The actin-related protein (Arp) 2/3 complex plays a central role in assembly of actin networks. Because distinct actin-based structures mediate diverse processes, many proteins are likely to make spatially and temporally regulated interactions with the Arp2/3 complex. We have isolated a new activator, Abp1p, which associates tightly with the yeast Arp2/3 complex. Abp1p contains two acidic sequences (DDW) similar to those found in SCAR/WASp proteins. We demonstrate that mutation of these sequences abolishes Arp2/3 complex activation in vitro. Genetic studies indicate that this activity is important for Abp1p functions in vivo. In contrast to SCAR/WASp proteins, Abp1p binds specifically to actin filaments, not monomers. Actin filament binding is mediated by the ADF/cofilin homology (ADF-H) domain of Abp1p and is required for Arp2/3 complex activation in vitro. We demonstrate that Abp1p recruits Arp2/3 complex to the sides of filaments, suggesting a novel mechanism of activation. Studies in yeast and mammalian cells indicate that Abp1p is involved functionally in endocytosis. Based on these results, we speculate that Abp1p may link Arp2/3-mediated actin assembly to a specific step in endocytosis.

Actin-Related Protein 2↗

PubMed2001

Metabolic redirection of carbon flow toward isoleucine by expressing a catabolic threonine dehydratase in a threonine-overproducing Corynebacterium glutamicum.

Carbon destined for lysine synthesis in Corynebacterium glutamicum ATCC 21799 can be diverted toward threonine by overexpression of genes encoding a feedback-insensitive homoserine dehydrogenase (hom(dr)) and homoserine kinase (thrB). We studied the effects of introducing two different threonine dehydratase genes into this threonine-producing system to gauge their effects on isoleucine production. Co-expression of hom(dr), thrB, and ilvA, which encodes a native threonine dehydratase, caused isoleucine to accumulate to a final concentration of 2.2+/-0.2 g l(-1), five-fold more than accumulates in the wild-type strain, and approximately twice as much as accumulates in the strain expressing only hom(dr) and thrB. Comparing these data with previous results, we found that overexpression of the three genes, hom(dr), thrB, and ilvA, in C. glutamicum ATCC 21799 is no better in terms of isoleucine production than the expression of a single gene, tdcB, encoding a catabolic threonine dehydratase from Escherichia coli. Co-expression of hom(dr), thrB, and tdcB, however, caused the concentration of isoleucine to increase 20-fold compared to the wild-type strain, about four times more than the corresponding ilvA-expressing strain. In this system, the apparent yield of isoleucine production was multiplied by a factor of two [2.1 mmol (g dry cell weight)(-1)]. While the balance of excreted metabolites showed that the carbon flow in this strain was completely redirected from the lysine pathway into the isoleucine pathway, it also showed that more pyruvate was diverted into amino acid synthesis.

Base Sequence↗

PubMed2001

Modular complexes that regulate actin assembly in budding yeast.

The actin cytoskeleton of budding yeast contains an extensive set of actin-associated proteins with conserved mammalian counterparts. For more than 20 years, yeast has been used as a model organism to dissect the in vivo functions of these factors, revealing an intricate web of genetic interactions in the cell. Now, a surge of biochemical reports is defining the physical interactions and activities of these proteins and providing mechanistic insights into their cellular roles. The emerging view is that most actin-associated proteins do not act alone but, rather, associate to form modular protein complexes that regulate actin assembly and organization.

Actins↗

PubMed2000

Functions and functional domains of the GTPase Cdc42p.

Cdc42p, a Rho family GTPase of the Ras superfamily, is a key regulator of cell polarity and morphogenesis in eukaryotes. Using 37 site-directed cdc42 mutants, we explored the functions and interactions of Cdc42p in the budding yeast Saccharomyces cerevisiae. Cytological and genetic analyses of these cdc42 mutants revealed novel and diverse phenotypes, showing that Cdc42p possesses at least two distinct essential functions and acts as a nodal point of cell polarity regulation in vivo. In addition, mapping the functional data for each cdc42 mutation onto a structural model of the protein revealed as functionally important a surface of Cdc42p that is distinct from the canonical protein-interacting domains (switch I, switch II, and the C terminus) identified previously in members of the Ras superfamily. This region overlaps with a region (alpha5-helix) recently predicted by structural models to be a specificity determinant for Cdc42p-protein interactions.

Amino Acid Sequence↗

PubMed1999

Aip1p interacts with cofilin to disassemble actin filaments.

Actin interacting protein 1 (Aip1) is a conserved component of the actin cytoskeleton first identified in a two-hybrid screen against yeast actin. Here, we report that Aip1p also interacts with the ubiquitous actin depolymerizing factor cofilin. A two-hybrid-based approach using cofilin and actin mutants identified residues necessary for the interaction of actin, cofilin, and Aip1p in an apparent ternary complex. Deletion of the AIP1 gene is lethal in combination with cofilin mutants or act1-159, an actin mutation that slows the rate of actin filament disassembly in vivo. Aip1p localizes to cortical actin patches in yeast cells, and this localization is disrupted by specific actin and cofilin mutations. Further, Aip1p is required to restrict cofilin localization to cortical patches. Finally, biochemical analyses show that Aip1p causes net depolymerization of actin filaments only in the presence of cofilin and that cofilin enhances binding of Aip1p to actin filaments. We conclude that Aip1p is a cofilin-associated protein that enhances the filament disassembly activity of cofilin and restricts cofilin localization to cortical actin patches.

Actin Depolymerizing Factors↗

PubMed1999

Expression of the Escherichia coli catabolic threonine dehydratase in Corynebacterium glutamicum and its effect on isoleucine production.

The catabolic or biodegradative threonine dehydratase (E.C. 4.2.1. 16) of Escherichia coli is an isoleucine feedback-resistant enzyme that catalyzes the degradation of threonine to alpha-ketobutyrate, the first reaction of the isoleucine pathway. We cloned and expressed this enzyme in Corynebacterium glutamicum. We found that while the native threonine dehydratase of C. glutamicum was totally inhibited by 15 mM isoleucine, the heterologous catabolic threonine dehydratase expressed in the same strain was much less sensitive to isoleucine; i.e., it retained 60% of its original activity even in the presence of 200 mM isoleucine. To determine whether expressing the catabolic threonine dehydratase (encoded by the tdcB gene) provided any benefit for isoleucine production compared to the native enzyme (encoded by the ilvA gene), fermentations were performed with the wild-type strain, an ilvA-overexpressing strain, and a tdcB-expressing strain. By expressing the heterologous catabolic threonine dehydratase in C. glutamicum, we were able to increase the production of isoleucine 50-fold, whereas overexpression of the native threonine dehydratase resulted in only a fourfold increase in isoleucine production. Carbon balance data showed that when just one enzyme, the catabolic threonine dehydratase, was overexpressed, 70% of the carbon available for the lysine pathway was redirected into the isoleucine pathway.

Biomass↗