Alpha-ketoglutarate semialdehyde dehydrogenase involved in the degradation of D-xylose, a major component of hemicelluloses such as xylan. Catalyzes the fifth reaction in the xylose utilization pathway through dehydratation of alpha-ketoglutarate semialdehyde (2,5-dioxopentanoate) into alpha-ketoglutarate. 2,5-dioxopentanoate + H2O + NADP(+) = 2-oxoglutarate + 2 H(+) + NADPH Carbohydrate metabolism; D-xylose degradation. Homotetramer. Transcriptionally up-regulated by both L-arabinose and D-xylose via the pentose-specific regulator XacR (PubMed:25141768, PubMed:19584053). Expression is repressed by glucose (PubMed:19584053). Impairs growth on D-xylose as sole energy and carbon substrate. Belongs to the aldehyde dehydrogenase family.