Identification of essential cysteine residues in 3-deoxy-D-arabino-heptulosonate-7-phosphate synthase from Corynebacterium glutamicum

Coenzyme preference of Streptococcus pyogenes δ1-pyrroline-5-carboxylate reductase: evidence supporting NADPH as the physiological electron donor

The streptococcal enzyme that catalyzes the last step in proline biosynthesis was heterologously expressed and the recombinant protein was purified to electrophoretic homogeneity and characterized thoroughly. As for δ1-pyrroline-5-carboxylate reductases from other sources, it was able to use either NADH or NADPH as the electron donor in vitro. However, with NADH the activity was markedly inhibited by physiological levels of NADP+. Results also strengthen the possibility that an unusual ordered substrate binding occurs, in which the dinucleotide binds last.

The best of all worlds or the best possible world? Developmental constraint in the evolution of beta-tubulin and the sperm tail axoneme

Through evolutionary history, some features of the phenotype show little variation. Stabilizing selection could produce this result, but the possibility also exists that a feature is conserved because it is developmentally constrained--only one or a few developmental mechanisms can produce that feature. We present experimental data documenting developmental constraint in the assembly of the motile sperm tail axoneme. The 9+2 microtubule architecture of the eukaryotic axoneme has been deeply conserved. We argue that the quality of motility supported by axonemes with this morphology explains their long conservation, rather than a developmental necessity for the 9+2 architecture. However, our functional tests in Drosophila spermatogenesis reveal considerable constraint in the coevolution of testis-specific beta-tubulin and the sperm tail axoneme. The evolution of testis beta-tubulins used in insect sperm tail axonemes is highly punctuated, indicating some pressure acting on their evolution. We provide a mechanistic explanation for their punctuated evolution by testing structure-function relationships between testis beta-tubulin and the motile axoneme in D. melanogaster. We discovered that a highly conserved sequence feature of beta-tubulins used in motile axonemes is needed to specify central pair formation. Second, our data suggest that cooperativity in the function of internal beta-tubulin amino acids is needed to support the long axonemes characteristic of Drosophila sperm tails. Thus, central pair formation constrains the evolution of the axoneme motif, and intramolecular cooperativity makes the evolution of the internal residues path dependent, which slows their evolution. Our results explain why a highly specialized beta-tubulin is needed to construct the Drosophila sperm tail axoneme. We conclude that these constraints have fixed testis-specific beta-tubulin identity in Drosophila.