A new type of thermoalkalophilic hydrolase of Paucimonas lemoignei with high specificity for amorphous polyesters of short chain-length hydroxyalkanoic acids
R. Handrick et al., A new type of thermoalkalophilic hydrolase of Paucimonas lemoignei with high specificity for amorphous polyesters of short chain-length hydroxyalkanoic acids, J BIOL CHEM, 276(39), 2001, pp. 36215-36224
A novel type of hydrolase was purified from culture fluid of Paucimonas (fo
rmerly Pseudomonas) lemoignei. Biochemical characterization revealed an unu
sual substrate specificity of the purified enzyme for amorphous poly((R)-3-
hydroxyalkanoates) (PHA) such as native granules of natural poly((R)-3-hydr
oxybutyrate) (PHB) or poly((R)-3-hydroxyvalerate) (PHV), artificial cholate
-coated granules of natural PHB or PHV, atactic poly((R,S)3-hydroxybutyrate
), and oligomers of (R)-3-hydroxybutyrate (3HB) with six or more 3HB units.
The enzyme has the unique property to recognize the physical state of the
polymeric substrate by discrimination between amorphous PHA (good substrate
) and denatured, partially crystalline PHA (no substrate). The pentamers of
3HB or 3HV were identified as the main products of enzymatic hydrolysis of
native PHB or PHV, respectively. No activity was found with any denatured
PHA, oligomers of (R)-3HB with five or less 3HB units, poly(6-hydroxyhexano
ate), substrates of lipases such as tributyrin or triolein, substrates for
amidases/nitrilases, DNA, RNA, casein, N-alpha -benzoyl-L-arginine-4-nitran
ilide, or starch. The purified enzyme (M-r 36,209) was remarkably stable an
d active at high temperature (60 degreesC), high pH (up to 12.0), low ionic
strength (distilled water), and in solvents (e.g. n-propyl alcohol). The d
epolymerase contained no essential SH groups or essential disulfide bridges
and was insensitive to high concentrations of ionic (SDS) and nonionic (Tr
iton and Tween) detergents. Characterization of the cloned structural gene
(phaZ7) and the DNA-deduced amino acid sequence revealed no homologies to a
ny PUB depolymerase or any other sequence of data banks except for a short
sequence related to the active site serine of serine hydrolases. A classifi
cation of the enzyme into a new family (family 9) of carboxyesterases (Arpi
gny, J. L., and Jaeger, YL-E. (1999) Biochem J. 343, 177-183) is suggested.