In oxygenic photosynthesis, conversion of solar energy to chemical energy is catalyzed by the<br/>pigment-protein complexes Photosystem II (PSII) and Photosystem I (PSI) embedded within the<br/>thylakoid membrane of photoautotrophs. The function of these pigment-protein complexes are<br/>conserved between all photoautotrophs, however, the oligomeric structure, as well as the<br/>spectroscopic properties of the PSI complex, differ. In early evolving photoautotrophs, PSI<br/>exists in a trimeric organization, but in later evolving species this was lost and PSI exists solely<br/>as a monomer. While the reasons for a change in oligomerization are not fully understood, one<br/>of the 11 subunits within cyanobacterial PSI, PsaL, is thought to be involved in trimerization<br/>through the coordination of a calcium ion in an adjacent monomer. Recently published<br/>structures have demonstrated that PSI complexes are capable of trimerization without<br/>coordinating the calcium ion within PsaL.<br/>5 Here we explore the role the calcium ion plays in both<br/>the oligomeric and spectroscopic properties in PSI isolated from Synechocystis sp. PCC 6803.

Polyketides are a wide ranging class of natural microbial products highly relevant to the pharmacological industry. As chemical synthesis of polyketides is quite challenging, significant effort has been made to understand the polyketide synthases (PKSs) responsible for their natural production. Native to Streptomyces, the aln biosynthetic gene cluster was recently characterized and encodes for an iterative type I polyketide synthase (iT1PKS). This iT1PKS produces both , and ,-double bond polyketides named allenomycins; however, the basis in which one bond is chosen over the other is not yet clear. The dehydratase domain, AlnB_DH, is thought to be solely responsible for catalyzing double bond formation. Elucidation of enzyme programming is the first step towards reprogramming AlnB_DH to produce novel industrially relevant products. The Nannenga lab has worked as collaborators to the Zhao lab at the University of Illinois at Urbana-Champaign to unravel AlnB_DH’s structure and mechanism. Here, mutant constructs of AlnB_DH are developed to elucidate enzyme structure and provide insight into active site machinery. The primary focus of this work is on the development of the mutant constructs themselves rather than the methods used for structural or mechanistic determination. Truncated constructs were successfully developed for crystallization and upon x-ray diffraction, a 2.45 Å resolution structure was determined. Point-mutated constructs were then developed based on structural insights, which identified H49, P58, and H62 as critical residues in active site machinery.