A cDNA cloned from Physarum polycephalum encodes new type of family 3 beta-glucosidase that is a fusion protein containing a calx-beta motif.
The microplasmodia of Physarum polycephalum express three types of beta-glucosidases: secretory enzyme, a soluble cytoplasmic enzyme and a membrane-bound enzyme. We are interested in the physiological role of three enzymes. We report the sequence of cDNA for membrane beta-glucosidase 1, which consists of 3825 nucleotides that includes an open reading frame encoding 1248 amino acids. The molecular weight of membrane beta-glucosidase 1 was calculated to be 131,843 based on the predicted amino acid composition. Glycosyl hydrolase family 3 N-terminal and C-terminal domains were found within the N-terminal half of the membrane beta-glucosidase 1 sequence and were highly homologous with the primary structures of fungal beta-glucosidases. Notably, the C-terminal half of membrane beta-glucosidase 1 contains two calx-beta motifs, which are known to be Ca(2+) binding domains in the Drosophila Na(+)/Ca(2+) exchanger; an RGD sequence, which is known to be a cell attachment sequence; and a transmembrane region. In this way, Physarum membrane beta-glucosidase 1 differs from all previously identified family 3 beta-glucosidases. In addition to cDNA for membrane beta-glucosidase 1, two other distinctly different mRNAs were also isolated. Two sequences were largely identical to cDNA for membrane beta-glucosidase 1, but included a long insert sequence having a stop codon, leading to truncation of their products, which could account for other beta-glucosidase forms occurred in Physarum poycephalum. Thus, the membrane beta-glucosidase is a new type family 3 enzyme fused with the Calx-beta domain. We propose that Calx-beta domain may modulate the beta-glucosidase activity in response to changes in the Ca(2+) concentration.
Maekawa
Akinori
A
Department of Biochemistry, Okayama University of Science, 1-1 Ridai-cho, Okayama 700-0005, Japan.
Hayase
Masato
M
Yubisui
Toshitsugu
T
Minami
Yoshiko
Y
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D015139:Blotting, Southern; D002462:Cell Membrane / Q000201:enzymology; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics*; D016054:DNA, Protozoan / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D018503:Genome, Protozoan / Q000235:genetics; D050576:Membrane Fusion Proteins / Q000737:chemistry* / Q000302:isolation & purification; D008969:Molecular Sequence Data; D010802:Phylogeny; D016839:Physarum polycephalum / Q000201:enzymology* / Q000235:genetics*; D017434:Protein Structure, Tertiary; D015800:Protozoan Proteins / Q000737:chemistry / Q000302:isolation & purification; D016415:Sequence Alignment; D013329:Structure-Activity Relationship; D001617:beta-Glucosidase / Q000737:chemistry* / Q000145:classification / Q000235:genetics* / Q000302:isolation & purification
D018076:DNA, Complementary; D016054:DNA, Protozoan; D050576:Membrane Fusion Proteins; D015800:Protozoan Proteins; D001617:beta-Glucosidase