in stereoselectivity result from residues which do not directly contact the substrate,
but have an indirect impact on the binding of triradylglycerols into the substrate
binding site.
Indirect, long-ranging effects are playing a role in all cases where residues far
away from the binding site mediate substrate recognition. They interact either by
changing the structure of the lipase and thus the shape of the binding site, by chan-
ging the physico-chemical properties of the protein, by changing its dynamics and
the flexibility of the binding site, or via long-range electrostatic interactions with the
substrate. While the role of residues directly interacting with substrate are fairly well
understood, the role of more distant residues is mostly obscure. Despite the successes
in engineering substrate binding sites, folding of a protein and the contribution of
individual residues to overall structure and dynamics remains an open question.
5.5 References
Adlercreutz, P. (1991), On the importance of the support material for enzymatic synthesis in organic
media. Support effects at controlled water activity.,Eur. J. Biochem 199 , 609–614.
Atomi, H., Bornscheuer, U., Soumanou, M.M., Beer, H.D., Wohlfahrt, G., Schmid, R.D. (1996),Oils-
Fats-Lipids, 21st World Congress Int. Soc. Fat. Res., P.J. Barnes, Bridgewater, pp. 49–50.
Beer, H.D., Wohlfahrt, G., McCarthy, J.E., Schomburg, D., Schmid, R.D.(1996), Analysis of the catalytic
mechanism of a fungal lipase using computer-aided design and structural mutants,Protein Eng. 9 ,
507–517.
96 5 Molecular Basis of Specificity and Stereoselectivity of Microbial Lipases
Figure 6. Ester substrate insn-1 orientation inRhizopus oryzaelipase (ROL, light gray) andRhizo-
mucor mieheilipase (RML, dark gray) (Scheib et al., 1999). The position of the G266 varies in both lipases
(Ca–Cadistance¼1.3 A ̊) due to the different position of E265 in ROL and T265 in RML, respectively
(horizontal arrow). Therefore, in ROL, the substrate binds deeper into the binding site than in RML
(C2RML–C2ROL¼0.9 A ̊). Hence, steric interactions between thesn-2 substituent and L258 are more
pronounced in ROL rather than RML (vertical arrow). (See color plate, page XVIII).