Disease relevance of BEM1

• Whole Genome Phage Display Selects for Proline-rich Boi Polypeptides against Bem1p [1].

High impact information on BEM1

• We also show that BUD5 interacts functionally with a gene, BEM1, that is required for bud formation [2].
• Bud emergence and incorporation of a plasma membrane sulfate permease activity stop quickly after a shift to 37 degrees C. Many of the mutants are thermoreversible; upon return to the permissive temperature (25 degrees C) the accumulated invertase is secreted [3].
• The predicted sequence of the BEM1 protein (Bem1p) reveals two copies of a domain (denoted SH3) that is found in many proteins associated with the cortical cytoskeleton and which may mediate binding to actin or some other component of the cell cortex [4].
• The sequence of Bem1p and the properties of mutants defective in this protein indicate that it may link the cytoskeleton to morphogenetic determinants on the cell surface [4].
• This morphological response requires the function of the cell polarity establishment protein Bem1p [5].

Biological context of BEM1

• Akr1p, which contains six ankyrin repeats, was identified during a screen for mutations that displayed synthetic lethality with a mutant allele of the bud emergence gene BEM1 [6].
• The same genetic screen identified BEM1, which encodes an SH3 domain protein required for polarized morphogenesis in response to pheromone, and a novel gene, designated MDG1 (multicopy suppressor of defective G-protein) [7].
• The yeast protein Bem1p, which bears two src homology region 3 (SH3) domains, is involved in cell polarization [8].
• Analysis using several truncated versions of BOI2 revealed that the COOH-terminal half, which contains the pleckstrin homology domain is essential for the function of Boi2p in cell growth, while the NH2-terminal half is not, and the NH2-terminal half might be required for modulating the function of Bem1p [8].
• The most frequently identified gene that arose from the bem1 synthetic-lethal screen was the bud-emergence gene BEM2 (Bender and Pringle. 1991. Mol. Cell Biol. 11:1295-1395), which is allelic with IPL2 (increase in ploidy; Chan and Botstein, 1993. Genetics. 135:677-691) [9].

Anatomical context of BEM1

• The SH3 domain-containing protein Bem1p is needed for normal bud emergence and mating projection formation, two processes that require asymmetric reorganizations of the cortical cytoskeleton in Saccharomyces cerevisiae [9].
• During in vitro fusion reactions, vacuoles from bem1Delta strains showed a strong reduction in the rate of lipid mixing when compared with vacuoles from the BEM1 parent [10].
• Localization of Bem1 to the incipient bud site requires activated Cdc42, and conversely, expression of Cdc42-GTP is sufficient to accumulate Bem1 at the plasma membrane [11].
• Bud emergence requires polarization of the cytoskeleton and secretory vesicles to a specific site on the cell surface [12].
• The PB1 (Phox and Bem 1) domain is a recently identified module that mediates formation of a heterodimeric complex with other PB1 domain, e.g. the complexes between the phagocyte oxidase activators p67phox and p40phox and between the yeast polarity proteins Bem1p and Cdc24p [13].

Associations of BEM1 with chemical compounds

• Mutational analysis revealed that the second SH3 domain from the NH2 terminus (SH3-2) of Bem1p is important for the functions of Bem1p in bud formation and in the suppression of the rho3 defect [8].
• Replacing Ser72 with Asp, to mimic phosphorylation at an optimal Cdk-consensus site located in the first SH3 domain of Bem1p, suppressed vacuolar fragmentation in cells lacking Cln3p [14].
• Mutation of tandem proline-rich (PxxP) motifs in this region disrupts Bem1 binding, suggesting that it serves as a ligand for a Bem1 SH3 domain [15].
• These PB1 domains harbor either a conserved lysine residue on one side or an acidic OPCA (OPR/PC/AID) motif around the other side; the lysine of p67phox or Bem1p likely binds to the OPCA of p40phox or Cdc24p, respectively, via electrostatic interactions [13].
• The C-terminal PB1 domain of yeast cell division cycle 24 (CDC24p), a guanine-nucleotide exchange factor involved in cell polarity establishment, is known to interact with the PB1 domain occurring in bud emergence MSB1 interacting 1 (BEM1p) during the regulation of the yeast budding process via its OPR/PC/AID (OPCA) motif [16].

Physical interactions of BEM1

• Here, we present evidence that through its second SH3 domain, Bem1p binds to the structurally and functionally similar proteins Boi1p and Boi2p, each of which contain an SH3 and pleckstrin homology (PH) domain [17].
• Anchoring was restored by fusing the targeting domain to either the Cdc24p carboxyl-terminal PC domain that interacts with the Bem1p scaffold protein or the Cdc42p KKSKKCTIL membrane-anchoring domain [18].
• This PxxP region also binds another SH3 domain protein, Nbp2, but analysis of bem1Delta versus nbp2Delta strains shows that the signaling defects of PxxP mutants result from impaired binding to Bem1 rather than from impaired binding to Nbp2 [15].
• A Novel Cdc42-interacting Domain of the Yeast Polarity Establishment Protein Bem1: IMPLICATIONS FOR MODULATION OF MATING PHEROMONE SIGNALING [19].

Regulatory relationships of BEM1

• Bud emergence in Saccharomyces cerevisiae involves cell cycle-regulated reorganizations of cortical cytoskeletal elements and requires the action of the Rho (Ras homologous)-type GTPase Cdc42 [20].
• Using in vivo and in vitro assays, we found that Cln3p was unable to promote vacuole fusion in the absence of Bem1p or in the presence of a nonphosphorylatable Bem1p-Ser72Ala mutant [14].
• Interaction with the SH3 domain protein Bem1 regulates signaling by the Saccharomyces cerevisiae p21-activated kinase Ste20 [15].

Other interactions of BEM1

• The COOH-terminal 75 amino acids of Cdc24p, outside of the GEF domain, can interact with a portion of Bem1p that lacks both SH3 domains [9].
• Boi2p, which bound to SH3-2 Bem1p, was identified using the two-hybrid system [8].
• Interactions between the bud emergence proteins Bem1p and Bem2p and Rho-type GTPases in yeast [9].
• Two of them were identical with CDC42 and BEM1, bud site assembly genes involved in the process of bud emergence [21].
• In contrast, deletion of BEM1 resulted in decreased expression of FUS1, suggesting that Bem1p normally facilitates pheromone signaling [6].

Analytical, diagnostic and therapeutic context of BEM1

• Depending on yield, the linear PCR product could be used directly for transformation, or after first cloning into a suitable vector. bemA, a putative homologue of the Saccharomyces cerevisiae BEM1 gene was identified through sequence comparison [22].
• The refined model was validated by site-directed mutagenesis on both Bem1 and Cdc24 [23].
• Target Bem1p was a doubly-tagged recombinant, Bem1([Asn142-Ile551]), which strongly interacts in ELISA with a C-terminal 75 amino acids polypeptide from Cdc24p exposed on phage [1].

References