Characterization of the family of Mistic homologues.
BACKGROUND
Mistic is a unique Bacillus subtilis protein with virtually no detectable homologues in GenBank, which appears to integrate into the bacterial membrane despite an overall hydrophilic composition. These unusual properties have been shown to be useful for high-yield recombinant expression of other membrane proteins through fusion to the C-terminus of Mistic. To better understand the structure and function of Mistic, we systematically searched for and characterized homologous proteins among closely related bacteria.


RESULTS
Three homologues of Mistic were found with 62% to 93% residue identity, all only 84 residues in length, corresponding to the C-terminal residues of B. subtilis Mistic. In every case, the Mistic gene was found partially overlapping a downstream gene for a K+ channel protein. Residue variation amongst these sequences is restricted to loop regions of the protein's structure, suggesting that secondary structure elements and overall fold have been conserved. Additionally, all three homologues retain the functional ability to chaperone fusion partners to the membrane.


CONCLUSIONS
The functional core of Mistic consists of 84 moderately conserved residues that are sufficient for membrane targeting and integration. Understanding the minimal structural and chemical complexity of Mistic will lead to insights into the mechanistic underpinnings of Mistic-chaperoned membrane integration, as well as how to optimize its use for the recombinant heterologous expression of other integral membrane proteins of interest.
Roosild
Tarmo P
TP
Structural Biology Laboratory, The Salk Institute for Biological Studies, La Jolla, California 92037, USA. roosild@earthlink.net
Vega
Mark
M
Castronovo
Samantha
S
Choe
Senyon
S
D000595:Amino Acid Sequence; D000596:Amino Acids / Q000737:chemistry; D001412:Bacillus subtilis / Q000737:chemistry* / Q000235:genetics; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D003001:Cloning, Molecular; D017124:Conserved Sequence / Q000235:genetics; D005798:Genes, Bacterial / Q000235:genetics; D018832:Molecular Chaperones / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D013329:Structure-Activity Relationship
D000596:Amino Acids; D001426:Bacterial Proteins; D018832:Molecular Chaperones