Hydroxynitrile lyase from rubber tree ( Hb HNL) shares 45% identical amino acid residues with the homologous esterase from tobacco, SABP2, but the two enzymes catalyze different reactions. The x-ray structures reveal a serine-histidine-aspartate catalytic triad in both enzymes along with several differing amino acid residues within the active site. Previous exchange of three amino acid residues in the active site of Hb HNL with the corresponding amino acid residue in SABP2 (T11G-E79H-K236M) created variant HNL3, which showed low esterase activity toward p-nitrophenyl acetate. Further structure comparison reveals additional differences surrounding the active site. Hb HNL contains an improperly positioned oxyanion hole residue and differing solvation of the catalytic aspartate. We hypothesized that correcting these structural differences would impart good esterase activity on the corresponding HbHNL variant. To predict the amino acid substitutions needed to correct the structure, we calculated shortest path maps for both Hb HNL and SABP2, which reveal correlated movements of amino acids in the two enzymes. Replacing four amino acid residues (C81L-N104T-V106F-G176S) whose movements are connected to the movements of the catalytic residues yielded variant HNL7TV (stabilizing substitution H103V was also added), which showed an esterase catalytic efficiency comparable to that of SABP2. The x-ray structure of an intermediate variant, HNL6V, showed an altered solvation of the catalytic aspartate and a partially corrected oxyanion hole. This dramatic increase in catalytic efficiency demonstrates the ability of shortest path maps to predict which residues outside the active site contribute to catalytic activity.
Title: Comparison of Five Protein Engineering Strategies for Stabilizing an alpha/beta-Hydrolase Jones BJ, Lim HY, Huang J, Kazlauskas RJ Ref: Biochemistry, 56:6521, 2017 : PubMed
A review of the previous stabilization of alpha/beta-hydrolase fold enzymes revealed many different strategies, but no comparison of strategies on the same enzyme. For this reason, we compared five strategies to identify stabilizing mutations in a model alpha/beta-hydrolase fold enzyme, salicylic acid binding protein 2, to reversible denaturation by urea and to irreversible denaturation by heat. The five strategies included one location agnostic approach (random mutagenesis using error-prone polymerase chain reaction), two structure-based approaches [computational design (Rosetta, FoldX) and mutation of flexible regions], and two sequence-based approaches (addition of proline at locations where a more stable homologue has proline and mutation to consensus). All strategies identified stabilizing mutations, but the best balance of success rate, degree of stabilization, and ease of implementation was mutation to consensus. A web-based automated program that predicts substitutions needed to mutate to consensus is available at http://kazlab.umn.edu .
Title: Population pharmacokinetics of CPT-11 (irinotecan) in gastric cancer patients with peritoneal seeding after its intraperitoneal administration Ahn BJ, Choi MK, Park YS, Lee J, Park SH, Park JO, Lim HY, Kang WK, Ko JW, Yim DS Ref: European Journal of Clinical Pharmacology, 66:1235, 2010 : PubMed
PURPOSE: It is well known that CPT-11 (irinotecan) is biotransformed to its active metabolite, SN-38, by carboxylesterase in the liver and other tissues. However, little is known about its pharmacokinetics (PK) when administered intraperitoneally. The aim of our study was to develop a population pharmacokinetic model for CPT-11 and SN-38 following the intraperitoneal (IP) administration of CPT-11. METHODS: Pharmacokinetic data obtained from 16 gastric adenocarcinoma patients with peritoneal seeding were used. Administered doses ranged from 50 to 250 mg/m(2). To measure CPT-11 and SN-38 levels, we collected samples of peritoneal fluid, plasma and urine 0, 0.5, 1.5, 2, 3.5, 8, 12, 25.5, 49 and 56 h after IP infusion. Several multicompartmental pharmacokinetic models were tested for CPT-11 and SN-38 in the sampled peritoneal fluid, plasma and urine. NONMEM ver. 6 was used throughout the model-building process. RESULTS: Peak concentrations were achieved earlier for peritoneal SN-38 than for plasma SN-38. The apparent metabolic clearance of peritoneal and plasma CPT-11 to peritoneal and plasma SN-38 accounted for 0.2 and 7.3% of the total clearance of peritoneal and plasma CPT-11, respectively. The typical values of steady-state volume of distribution (Vss) (46.6 L/m(2)), inter-compartment clearance (6.70 L/h/m(2)) and clearance (16.0 L/h/m(2)) for plasma CPT-11 were estimated in a two-compartment PK model. CONCLUSIONS: Our results demonstrate that a small fraction of intraperitoneally administered CPT-11 was metabolized in situ to active SN-38 and that the Vss of plasma CPT-11 following IP administration in our patient cohort was lower than that estimated in previous reports following the intravenous administration of CPT-11.
