Ketoisovalerate reductase; part of the gene cluster that mediates the biosynthesis of beauvericin (BEA), a non-ribosomal cyclic hexadepsipeptide that shows antibiotic, antifungal, insecticidal, and cancer cell antiproliferative and antihaptotactic activity (PubMed:23832252, PubMed:22916830). Ketoisovalerate reductase BEA2 catalyzes the NADPH-specific reduction of ketoisovaleric acid to hydroxyisovalerate, a precursor for beauvericin biosynthesis (PubMed:23832252, PubMed:22916830). The nonribosomal cyclodepsipeptide synthetase BEA1 then catalyzes the formation of beauvericin via condensation and cyclization of 3 dipeptidol monomers, each composed of one unit of hydroxyisovalerate and one unit of N-methyl-phenylalanine (By similarity). (R)-2-hydroxy-3-methylbutyrate + NADP(+) = 3-methyl-2-oxobutanoate + H(+) + NADPH The reductase activity is increased by Mg(2+) (195%), Ca(2+) (169%) and slightly increased by K(+) (123%) (PubMed:22916830). The reduction activity is inhibited by Fe(2+) and Co(2+), and almost totally inhibited by Cu(2+), Mn(2+), Zn(2+) and Fe(3+) (from 3% to 9% residual activity respectively) (PubMed:22916830). The chelating agent EDTA had little effect, suggesting Mg(2+) and Ca(2+) are not determining factors, though they could promote the reductase enzyme activity (PubMed:22916830). Optimum pH is 7.5. Optimum temperature is 35 degrees Celsius. Belongs to the ketopantoate reductase family.