Conformational changes associated with cofactor/substrate binding of 6-phosphogluconate dehydrogenase from Escherichia coli and Klebsiella pneumoniae: Implications for enzyme mechanism.

6-Phosphogluconate dehydrogenase (6PGDH), the third enzyme of the pentose phosphate pathway, catalyzes the oxidative decarboxylation of 6-phosphogluconate, making ribulose 5-phosphate, along with the reduction of NADP(+) to NADPH and the release of CO(2). Here, we report the first apo-form crystal structure of the pathogenic Klebsiella pneumoniae 6PGDH (Kp6PGDH) and the structures of the highly homologous Escherichia coli K12 6PGDH (Ec6PGDH) complexed with substrate, substrate/NADPH and glucose at high resolution. The binding of NADPH to one subunit of the homodimeric structure triggered a 10 degrees rotation and resulting in a 7A movement of the coenzyme-binding domain.

Assembling microtubules disintegrate the postsynaptic density in vitro.

The postsynaptic density (PSD), a disk-shaped protein aggregation of several hundred nm in diameter, plays important roles in the signal transduction and molecular organization of the excitatory synapses in mammalian CNS. The PSD resides in the microfilament-enriched cytoplasm of dendritic spines where the transient appearance of microtubules has been reported. When PSD isolated from porcine brain was incubated with polymerizing alpha,beta-tubulins, its turbidity became greater than that of the original PSD, suggesting that the PSD's structure was altered upon incubating with assembling microtubules.