Guanine deaminase in developing rat brain

Identification of small molecule compounds with higher binding affinity to guanine deaminase (cypin) than guanine

Guanine deaminase (GDA; cypin) is an important metalloenzyme that processes the first step in purine catabolism, converting guanine to xanthine by hydrolytic deamination. In higher eukaryotes, GDA also plays an important role in the development of neuronal morphology by regulating dendritic arborization. In addition to its role in the maturing brain, GDA is thought to be involved in proper liver function since increased levels of GDA activity have been correlated with liver disease and transplant rejection. Although mammalian GDA is an attractive and potential drug target for treatment of both liver diseases and cognitive disorders, prospective novel inhibitors and/or activators of this enzyme have not been actively pursued. In this study, we employed the combination of protein structure analysis and experimental kinetic studies to seek novel potential ligands for human guanine deaminase. Using virtual screening and biochemical analysis, we identified common small molecule compounds that demonstrate a higher binding affinity to GDA than does guanine. In vitro analysis demonstrates that these compounds inhibit guanine deamination, and more surprisingly, affect GDA (cypin)-mediated microtubule assembly. The results in this study provide evidence that an in silico drug discovery strategy coupled with in vitro validation assays can be successfully implemented to discover compounds that may possess therapeutic value for the treatment of diseases and disorders where GDA activity is abnormal.

Deficiency of a naturally occurring protein inhibitor in brain of clinically 'brain damaged' newborn human infants - a possible cause of mental retardation?

The presence of an inhibitor of guanine deaminase in the 'heavy' mito-chondrial fractions of rat brain homogenates has been reported. The results of the present study, using brain homogenates from normal infants who died between ages 1-6 months, low birth weight infants who were brain damaged and died between ages 2 days-4 months and premature (7-8 months pregnancy) infants, who were considered clinical cases with acute brain damage and died 1-3 days after birth, indicate that while normal human brain contains the inhibitory material, it is conspicuously absent from the particulate fractions of brain damaged low birth weight and premature infants. Since brain damage at birth in an infant could result in mental retardation of some kind on development, a possible relationship between deficiency or absence of the inhibitory material of guanine deaminase in human brain and mental retardation is suggested.