PyrH and PrnB crystal structures

Abstract

Determination of the three-dimensional structure of enzymes at atomic resolution is a key prerequisite for elucidation of molecular mechanisms of catalysis and catalysis mechanism prediction. X-ray protein crystallography is the most widely used method today for determining protein structures. In this thesis we describe the expression, purification, crystallization and structure solution of two new enzymes: PyrH and PrnB. PyrH is a member of the new emerging family of FADH dependent tryptophan halogenases. It catalyzes the regioselective halogenation of tryptophan at the C-5 position of the indole ring. Elucidation of its structure (Chapter 2) and comparison with PrnA, aregioselective 7th tryptophan halogenase whose structure has already been solved confirmed the proposed mechanism of action for this class of enzymes. PrnB is the only enzyme known to perform exquisite and peculiar ring rearrangement chemistry: it converts 7-Cl-tryptophan and tryptophan into respectively monodechloroaminopyrrolnitrin and aminophenylpyrrole. We developed a method for expression and purification of milligrams of pure and homogeneous recombinant PrnB (Chapter 3). We identified suitable crystallization conditions and determined PrnB structure (Chapter 4). Analysis of the PrnB structure helped us to propose a reaction mechanism for this unique enzyme.