Dihydroxyacetone (Dha) in hemiaminal linkage to the active site of dihydroxyacetone kinase (Swiss-Prot P76015). The hemiaminal is formed between the carbonyl carbon of Dha and the imidazole nitrogen of histidin-230 (HOCH₃-COH(-NHis)-CH₃OH). The substrate is further stabilized by a network of hydrogen bonds. The covalent bond does not participate in catalysis but is a means to discriminate between the chemically reactive Dha and the structurally similar but inert glycerol.
Dha kinase can mop up microM concentrations of potentially toxic Dha in the presence of glycerol, a compatible solute which may be produced to high concentrations under salt and cold stress.

This work was carried out in the groups of Prof. Bernhard Erni / Prof. Ulrich Baumann.

References:

• C. Siebold, L. Fernando García-Alles, B. Erni, U. Baumann;
  "A mechanism of covalent substrate binding in the x-ray structure of subunit K of the Escherichia coli dihydroxyacetone kinase "
  Proc. Natl. Acad. Sci. USA, 100, 8188-8192, (2003); doi:10.1073/pnas.0932787100.