7s3v | pdb_00007s3v
Structure of HsKYNase_66, an evolved variant of human kynureninase with greatly increased activity towards kynurenine
Structural highlights
DiseaseKYNU_HUMAN Note=Xanthurenic aciduria manifesting as massive urinary excretion of large amounts of kynurenine, 3-hydroxykynurenine and xanthurenic acid has been observed in an individual carrying a homozygous missense change in KYNU (PubMed:17334708). The urinary pattern in the patient suggests kynureninase deficiency and a block in the conversion of kynurenine and 3-hydroxykynurenine to anthranilate and 3-hydroxyanthranilate, respectively.[HAMAP-Rule:MF_03017] FunctionKYNU_HUMAN Catalyzes the cleavage of L-kynurenine (L-Kyn) and L-3-hydroxykynurenine (L-3OHKyn) into anthranilic acid (AA) and 3-hydroxyanthranilic acid (3-OHAA), respectively. Has a preference for the L-3-hydroxy form. Also has cysteine-conjugate-beta-lyase activity.[HAMAP-Rule:MF_03017] Publication Abstract from PubMedThe Trp metabolite kynurenine (KYN) accumulates in numerous solid tumours and mediates potent immunosuppression. Bacterial kynureninases (KYNases), which preferentially degrade kynurenine, can relieve immunosuppression in multiple cancer models, but immunogenicity concerns preclude their clinical use, while the human enzyme (HsKYNase) has very low activity for kynurenine and shows no therapeutic effect. Using fitness selections, we evolved a HsKYNase variant with 27-fold higher activity, beyond which exploration of >30 evolutionary trajectories involving the interrogation of >10(9) variants led to no further improvements. Introduction of two amino acid substitutions conserved in bacterial KYNases reduced enzyme fitness but potentiated rapid evolution of variants with ~500-fold improved activity and reversed substrate specificity, resulting in an enzyme capable of mediating strong anti-tumour effects in mice. Pre-steady-state kinetics revealed a switch in rate-determining step attributable to changes in both enzyme structure and conformational dynamics. Apart from its clinical significance, our work highlights how rationally designed substitutions can potentiate trajectories that overcome barriers in protein evolution. Bypassing evolutionary dead ends and switching the rate-limiting step of a human immunotherapeutic enzyme.,Blazeck J, Karamitros CS, Ford K, Somody C, Qerqez A, Murray K, Burkholder NT, Marshall N, Sivakumar A, Lu WC, Tan B, Lamb C, Tanno Y, Siddiqui MY, Ashoura N, Coma S, Zhang XM, McGovern K, Kumada Y, Zhang YJ, Manfredi M, Johnson KA, D'Arcy S, Stone E, Georgiou G Nat Catal. 2022 Oct;5(10):952-967. doi: 10.1038/s41929-022-00856-6. Epub 2022 Oct , 19. PMID:36465553[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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