Functional Constraint in the Evolution of Spermtail Axonemes

University Of Dayton, Dayton OH

Investigators

Abstract

Proteins are the fundamental building blocks of all life, and changes in proteins over evolutionary time have resulted in the incredible diversity of life on earth. Because the function of any particular protein is dictated by the sequence of its amino acids, any alterations in sequence have the potential of modifying the protein's function. The need to maintain proper functionality of a particular protein, therefore, puts constraints on the extent to which a protein sequence can diverge during evolution. This focus of this project is B2-tubulin, a major structural component of the spermtail of the fruit fly, Drosophila melanogaster. Within the spermtail, B2-tubulin is organized into an array of precisely ordered filaments in a structure known as the axoneme, which is required for sperm motility. Slight alterations in its amino acid composition cause the Drosophila spermtail to fall apart, raising the question of how B2 was able to evolve in other fly species while maintaining a functional spermtail. This project involves a comparative study of the B2 tubulins from various fly species designed to identify features of the B2-tubulin amino acid sequence responsible for its assembly into axonemes and for sperm motility. The B2-tubulin gene will be cloned from different species of flies, and the evolution of the B2 amino acid sequence will be detailed. Based on this information, recombinant DNA technology will be used to engineer modified forms of B2-tubulin. These modified forms of B2-tubulin will be expressed in transgenic flies to determine how changes in the B2-tubulin amino acid composition affect its ability to function in vivo. This research contributes new understanding to the process by which subtle evolutionary changes in amino acid sequence contribute to divergent functional properties of a protein. These experiments will involve both undergraduate and graduate students who will gain research training in molecular biology and microscopic techniques.