High impact information on MID1

• Single-channel analyses with cell-attached patches revealed that Mid1 acts as a calcium-permeable, cation-selective stretch-activated channel with a conductance of 32 picosiemens at 150 millimolar cesium chloride in the pipette [1].
• No genetic interactions were found between mid2 and the related gene mid1 [2].
• The depleted ER also stimulated Ca2+ influx at the plasma membrane through the Cch1p-Mid1p Ca2+ channel and another system [3].
• Association of green fluorescent protein-Mid1 with microtubules in living cells was perturbed by inhibitors of MAP kinase activation [4].
• A screen for yeast mutants specifically defective in the high-affinity Ca(2+) uptake system revealed two genes, CCH1 and MID1, previously implicated in Ca(2+) influx in response to mating pheromones [5].

Biological context of MID1

• The mid1-1 spa2Delta double mutant did not have the mid phenotype, indicating that SPA2 is epistatic to MID1 [6].
• Strains defective in a putative plasma membrane calcium channel (Cch1-Mid1) were modestly more susceptible to fluconazole but showed a significant loss of viability upon prolonged fluconazole exposure, suggesting that calcium signaling is required for survival of azole stress in C. glabrata [7].
• Therefore, we suggest that Mid1 function is influenced by Spa2 function through polarized morphogenesis [6].
• To solve this problem, we identified the mutation sites of mid1 mutant alleles generated by in vivo ethyl methanesulfonate mutagenesis and found that two mid1 alleles have nonsense mutations at the codon for Trp(441), generating a truncated Mid1 protein lacking two-thirds of the intracellular carboxyl-terminal region from Asn(389) to Thr(548) [8].
• Hexose phosphorylation and the putative calcium channel component Mid1p are required for the hexose-induced transient elevation of cytosolic calcium response in Saccharomyces cerevisiae [9].

Anatomical context of MID1

• This mutation defines a new gene, designated MID1, which encodes an N-glycosylated, integral plasma membrane protein with 548 amino acid residues [10].
• The region from H1 to H3 is required for the localization of Mid1 in the plasma and ER membranes [11].
• The yeast Mid1 protein with an apparent molecular mass of 100 kDa is required for Ca2+ influx stimulated by the mating pheromone and by a capacitative calcium entrylike mechanism acting in response to Ca2+ depletion from the endoplasmic reticulum (ER) and functions as a stretch-activated Ca2+ -permeable channel when expressed in mammalian cells [12].

Associations of MID1 with chemical compounds

• Uptake of the extracellular Ca2+ is inhibited by caffeine and reduced in strains deleted for the mid1 gene, but not in cells deleted for cch1 [13].
• These results clearly indicate that the carboxyl-terminal domain including the cysteine residues is important for Mid1 function [8].
• Mutant Mid1 proteins lacking the whole H3 or H4 segment, H3De or H4De, did not complement the lethality and low Ca(2+) accumulation activity of the mid1 mutant, although their localization and contents appeared to be normal, indicating that H3 and H4 are required for Mid1 function itself [14].
• This increase was largely abolished by addition of EGTA to the medium or in cells lacking Mid1 or Cch1, components of the high affinity cell membrane calcium channel [15].

Other interactions of MID1

• Expression of Cch1p and Mid1p was not affected in pmr1 mutants [5].
• Finally, trafficking of Mid1-GFP to the plasma membrane was dependent on the N-glycosylation of Mid1 and the transporter protein Sec12 [11].
• Ste12p activation had no effect on Cch1p or Mid1p abundance, suggesting the involvement of another target of Ste12p in HACS stimulation [16].
• Intracellular fluorescence images for Mid1 were the same as those for the ER marker protein Sec71 but quite different from those of the Golgi protein Ypt1 [12].
• Sorbate resistance is, however, elevated with the loss of the Yap5 transcription factor; with single losses of two B-type cyclins (Clb3p, Clb5p); and with loss of a plasma membrane calcium channel activated by endoplasmic reticulum stress (Cch1p/Mid1p) [17].

Analytical, diagnostic and therapeutic context of MID1

• Molecular dissection of the hydrophobic segments H3 and H4 of the yeast Ca2+ channel component Mid1 [14].
• To identify the important regions or amino acid residues necessary for Mid1 function, we employed in vitro site-directed mutagenesis on H3 and H4 of Mid1 and expressed the resulting mutant genes in a mid1 null mutant to examine whether the mutant gene products are functional or not in vivo [14].
• However, we find that the Cch1p-Mid1p high-affinity Ca(2+) influx system (HACS) contributes very little to signaling or survival after treatment with alpha-factor in rich media [16].
• In a protein database, we found a Schizosaccharomyces pombe gene whose predicted protein shows 26% identical and 62% similar to the Mid1 channel in amino acid sequence. cDNA derived from this gene, designated yam8(+), was isolated by reverse transcription-polymerase chain reaction (RT-PCR) [18].

References