Hydrolases in Polymer Chemistry: Part III: Synthesis and Limited Surface Hydrolysis of Polyesters and Other Polymers - Enzymatic Polymerisation - page 118

BAA01524_Pseudomonas sp. NK87 (EII) (0.3321)
BAA05087_Arthrodbacter sp. KI723T1 (EII) (0.0564)
BAA05089_Arthrobacter sp. KI723T1 (EII') (0.0609)
BAA05088_Arthrobacter sp. KI723T1 (EIII) (0.4630)
CAC93613_Stenotrophomonas maltophilia (0.3831)
069768_Pseudomonas putida (0.3627)
BAA05090_Arthrobacter sp. KI723T1 (EI) (0.0000)
P13398_Pseudomonas sp. NK87 (EI) (0.0000)
Q092U4_Stigmatella aurantiaca DW4/3-1 (6-aminohexanoate-cyclic-dimer hydrolase) (0.2373)
Q1D8G0_Myxococcus xanthus DK 1622 (amidase familiy protein) (0.1859)
Q21Z32_Rhodopseudomonas palustris HaA2 (amidase) (0.2347)
MS fragments (0.0065)
YP_119043_Nocardia farcinica IFM 10152 (0.0083)
Q396E7_Burkholderia sp. 383 (amidase) (0.2397)
Q5LQG3_Silicibacter pomeroyi (6-aminohexanoate-cyclic-dimer hydrolase) (0.2761

Fig. 1 Phylogenetic tree based on amino acid sequences of the polyamidase from Nocardia
farcinica and other highly homologous bacterial amidases as well as amidases with substrate speci-
ficity for 6-aminohexanoate oligomers [ 20 ]

3 PET Hydrolases

As for PA-hydrolysing enzymes, representatives from different enzyme classes
including lipases, esterases, cutinases and proteases have been demonstrated to hy-
drolyse PET and are termed PET hydrolases here. Searching for PET hydrolases
in nature, the first choice was the investigation of enzymes that hydrolyse the hy-
drophobic plant polyester cutin. Cutin from the plant cuticle consists of oxygenated
C16 and C18 fatty acids crosslinked by ester bonds [ 39 ] and is essential for plant
protection. Cutin degradation by cutinases is one of the first steps in the infection
of plants [ 40 ] . Cutinases show both exo -and endo -esterase activity [ 41 ] and have
first been investigated from F. solani pisi growing on cutin as a carbon source [ 42 ] .
Cutin oligomers have been suggested to induce production of these enzymes [ 43 ].
Interestingly, some PET-hydrolyzing enzyme activities were likewise inducible
by addition of cutin [ 44 , 45 ]. A number of fungal cutinases, such as from F. solani
and Fusarium oxysporum [ 13 , 46 , 47 ] ; Aspergillus oryzae , Aspergillus niger and
Aspergillus nomius [ 48 - 50 ] ; Humicola sp. and Humicola insolens [ 47 , 51 , 52 ]; and
from Penicillium citrinum [ 45 ], have shown PET hydrolase activity. Cutinases carry
their active site at the surface of the protein, which is essential for endo -wise hydrol-
ysis of polymers. Recently, a comparison of the substrate specificities and structures
of the F. solani and A. oryzae cutinases revealed a preference of the latter enzyme
to hydrolyse longer chain substrates. This is probably due to a deep continuous
groove extending across the active site, in contrast to that of F. solani with a shallow
and interrupted groove (Fig. 2 ) . Consequently, the A. oryzae cutinase showed higher
activity on the polyester poly( -caprolactone) [ 53 ]. Cutinases are also widespread

in bacteria, and representatives from Thermobifida fusca [ 2 , 15 , 44 , 54 ], Ther-
mobifida alba [ 52 ]and Pseudomonas mendocina [ 18 ] have shown PET hydrolase
activity.
In addition to cutinases, various lipases, such as from C. antarctica , Candida
sp. [ 13 , 47 ], Thermomyces lanuginosus [ 2 , 14 , 15 , 55 , 56 ] , Burkholderia (formerly
Pseudomonas ) cepacia [ 57 ] and esterases from Pseudomonas sp. (serine esterase)
[ 58 ]and Bacillus sp. (nitrobenzyl esterases) [ 59 , 60 ] , have shown PET hydrolase

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