Download citation
Acta Cryst. (2014). A70, C429
Download citation

link to html
Mycobacteria have an unusual redundancy of six putative carboxyltransferase genes that form high-molecular weight holo acyl coenzyme A carboxylase complexes with a complementary set of three biotin carboxylase genes. Most of these enzyme complexes use small fatty acid coenzyme A esters as substrate, to allow their extension by one methylene group via a carboxybiotin-mediated α-carboxylation reaction. Redundant occurrence of these complexes was assumed to be related to highly complex enzymatic requirements in lipid biosynthesis, as the mycobacterial thick cell wall comprises unusual very long chain fatty acids, including mycolic acid. We have solved two high-resolution crystal structures of the 350 kDa hexameric assemblies of two different acyl coenzyme A carboxylase hexameric assemblies, AccD5 and AccD6 [1; Anandhakrishnan et al., unpublished], and characterized these enzyme complexes functionally. In a second step we investigated the acyl coenzyme A carboxylase complex AccD1-AccA1 from Mycobacteria tuberculosis with hitherto unknown function. By using a metabolomics approach we found that AccD1-AccA1 is involved in branched amino acid catabolism, which was not investigated in mycobacteria before [Ehebauer et al, unpublished. Using an in vitro assay, we show that the enzyme complex uses methylcrotonyl coenzyme A as substrate]. We determined the overall architecture of the 700 kDa AccD1-AccA1 complex to be formed from three layers of a central AccD1 hexameric ring, flanked by two distal tiers composed of three AccA1 subunits each. Our electron microscopy data match the overall dimensions of a methylcrotonyl coenzyme A holo complex with known structure and thus support our functional findings. Our data suggest a unique functional role of the AccD1-AccA1 complex within the Mycobacterium tuberculosis acyl coenzyme A carboxylase interactome. Ultimately, it is our goal to solve this and related structures of ACCase holo complexes by high-resolution crystallography as well. The abstract is dedicated to Louis Delbaere with whom I shared time during my PhD at the University of Basel, Switzerland.

Download citation
Acta Cryst. (2014). A70, C1170
Download citation

link to html
The High Chlorophyll Fluorescence 136 protein (HCF136) is essential for the assembly and repair of Photosystem II (PSII) and its central reaction centre (RC)[1]. HCF136 is an abundant protein in the thylakoid lumen and has been suggested to directly interact with subunits of the RC. The multi-subunit pigment-protein PSII complex is imbedded in the thylakoid membrane of the oxygenic photosynthetic organisms, and responsible for water splitting during oxygenic photosynthesis. PSII harbours more than 20 different integral and peripheral membrane proteins and its assembly requires a high level of coordination[2]. Two proteins D1 (psbA) and D2 (psbD) form the core of the complex and bind most of the redox-active co-factors. The PSII RC contains, in addition to D1 and D2, the intrinsic PsbI subunit and cytochrome b559. Light is a harmful substrate and subunits are damaged during the water-splitting reaction. The largest irreversible damage is experienced by the central D1 protein that has the highest turnover rate of all thylakoid proteins. Analysis of mutated A. thaliana has identified HCF136 as an essential factor for PSII RC assembly and RC turnover and repair[3]. In order to gain functional and structural insight in the way the HCF136 protein is involved in the PSII repair cycle, we have cloned, expressed, purified and crystallized the HCF136 protein from A. thaliana. Here we present the structure of this doughnut shaped WD40 domain family protein determined at 1.67 Å resolution. Biochemical and biophysical analysis of HCF136 and components of the PSII RC are under way.
Follow Acta Cryst. A
Sign up for e-alerts
Follow Acta Cryst. on Twitter
Follow us on facebook
Sign up for RSS feeds