6M6T image
Entry Detail
PDB ID:
6M6T
Keywords:
Title:
Amylomaltase from Streptococcus agalactiae in complex with acarbose
Biological Source:
Source Organism:
Host Organism:
PDB Version:
Deposition Date:
2020-03-16
Release Date:
2021-03-31
Method Details:
Experimental Method:
Resolution:
2.75 Å
R-Value Free:
0.28
R-Value Work:
0.20
R-Value Observed:
0.20
Space Group:
P 21 21 21
Macromolecular Entities
Polymer Type:polypeptide(L)
Description:4-alpha-glucanotransferase
Chain IDs:A, B, C, D, E, F, G, H
Chain Length:507
Number of Molecules:8
Biological Source:Streptococcus agalactiae
Peptide-like Molecules
PRD_900007
PRD_900110
Primary Citation
Streptococcus agalactiae amylomaltase offers insight into the transglycosylation mechanism and the molecular basis of thermostability among amylomaltases.
Sci Rep 11 6740 6740 (2021)
PMID: 33762620 DOI: 10.1038/s41598-021-85769-3

Abstact

Amylomaltase (AM) catalyzes transglycosylation of starch to form linear or cyclic oligosaccharides with potential applications in biotechnology and industry. In the present work, a novel AM from the mesophilic bacterium Streptococcus agalactiae (SaAM), with 18-49% sequence identity to previously reported AMs, was characterized. Cyclization and disproportionation activities were observed with the optimum temperature of 30 °C and 40 °C, respectively. Structural determination of SaAM, the first crystal structure of small AMs from the mesophiles, revealed a glycosyl-enzyme intermediate derived from acarbose and a second acarbose molecule attacking the intermediate. This pre-transglycosylation conformation has never been before observed in AMs. Structural analysis suggests that thermostability in AMs might be mainly caused by an increase in salt bridges since SaAM has a lower number of salt bridges compared with AMs from the thermophiles. Increase in thermostability by mutation was performed. C446 was substituted with A/S/P. C446A showed higher activities and higher kcat/Km values for starch in comparison to the WT enzyme. C446S exhibited a 5 °C increase in optimum temperature and the threefold increase in half-life time at 45 °C, most likely resulting from H-bonding interactions. For all enzymes, the main large-ring cyclodextrin (LR-CD) products were CD24-CD26 with CD22 as the smallest. C446S produced more CD35-CD42, especially at a longer incubation time.

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Primary Citation of related structures