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J. Bacteriol., 07 1997, 4129-4137, Vol 179, No. 13
CL Bouma, J Reizer, A Reizer, SA Robrish and J Thompson
The Fusobacterium mortiferum malH gene, encoding 6-phospho-alpha-
glucosidase (maltose 6-phosphate hydrolase; EC 3.2.1.122), has been
isolated, characterized, and expressed in Escherichia coli. The relative
molecular weight of the polypeptide encoded by malH (441 residues; Mr of
49,718) was in agreement with the estimated value (approximately 49,000)
obtained by sodium dodecyl sulfate- polyacrylamide gel electrophoresis for
the enzyme purified from F. mortiferum. The N-terminal sequence of the MalH
protein obtained by Edman degradation corresponded to the first 32 amino
acids deduced from the malH sequence. The enzyme produced by the strain
carrying the cloned malH gene cleaved [U-14C]maltose 6-phosphate to glucose
6- phosphate (Glc6P) and glucose. The substrate analogs p-nitrophenyl-
alpha-D-glucopyranoside 6-phosphate (pNP alphaGlc6P) and 4-
methylumbelliferyl-alpha-D-glucopyranoside 6-phosphate (4MU alphaGlc6P)
were hydrolyzed to yield Glc6P and the yellow p-nitrophenolate and
fluorescent 4-methylumbelliferyl aglycons, respectively. The 6-phospho-
alpha-glucosidase expressed in E. coli (like the enzyme purified from F.
mortiferum) required Fe2+, Mn2+, Co2+, or Ni2+ for activity and was
inhibited in air. Synthesis of maltose 6-phosphate hydrolase from the
cloned malH gene in E. coli was modulated by addition of various sugars to
the growth medium. Computer-based analyses of MalH and its homologs
revealed that the phospho-alpha-glucosidase from F. mortiferum belongs to
the seven-member family 4 of the glycosylhydrolase superfamily. The cloned
2.2-kb Sau3AI DNA fragment from F. mortiferum contained a second partial
open reading frame of 83 residues (designated malB) that was located
immediately upstream of malH. The high degree of sequence identity of MalB
with IIB(Glc)-like proteins of the phosphoenol pyruvate dependent:sugar
phosphotransferase system suggests participation of MalB in translocation
of maltose and related alpha- glucosides in F. mortiferum.
Copyright © 1997, American Society for Microbiology
6-phospho-alpha-D-glucosidase from Fusobacterium mortiferum: cloning, expression, and assignment to family 4 of the glycosylhydrolases
School of Pharmacy, Texas Tech University, Amarillo 79106, USA.
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