A large number of antibiotics and other industrially important microbial secondary metabolites are synthesized by polyketide synthases (PKSs) and nonribosomal peptide synthetases (NRPSs). These multienzymatic complexes provide an enormous flexibility in formation of diverse chemical structures from simple substrates, such as carboxylic acids and amino acids. Modular PKSs and NRPSs, often referred to as megasynthases, have brought about a special interest due to the colinearity between enzymatic domains in the proteins working as an “assembly line” and the chain elongation and modification steps. Extensive efforts toward modified compound biosynthesis by changing organization of PKS and NRPS domains in a combinatorial manner laid good grounds for rational design of new structures and their controllable biosynthesis as proposed by the synthetic biology approach. Despite undeniable progress made in this field, the yield of such “unnatural” natural products is often not satisfactory. Here, we focus on type II thioesterases (TEIIs)—discrete hydrolytic enzymes often encoded within PKS and NRPS gene clusters which can be used to enhance product yield. We review diverse roles of TEIIs (removal of aberrant residues blocking the megasynthase, participation in substrate selection, intermediate, and product release) and discuss their application in new biosynthetic systems utilizing PKS and NRPS parts.

Practical problems of the reproduction of the orientation distribution function (ODF) from pole figures (PFs) using discrete methods (with special attention paid to Imhof's method) are analysed.A new variant of the iteration method for the determination of the ODF in arbitrarily defined size of cells in the orientation space, is suggested. The special case, in which the centro-symmetrical equivalency of the PFs is induced by the elements of proper rotations in crystal symmetry, is considered.Es werden praktische Probleme der Reproduktion der Orientierungsverteilungsfunktion (OVF) aus Polfiguren (PFn) bei Anwendung diskreter Methoden (bei besonderer Beachtung der Imhof Methode) analysiert. Eine neue Variante des Iterationsverfahrens fiir die Bestimmung des OVF mit einer Wahlfreiheit der ZellengroDe im Orientierungsraum wird vorgeschlagen. Es wird ein Spezialfall betrachtet, in dem Elemente der eigentlichen Drehungen in der Kristallsymmetrie eine zentrosymmetrische Gleichwertigkeit in den PFn induzieren.

The chromosome of Streptomyces coelicolor A3(2), a model organism for the genus Streptomyces, contains a cryptic type I polyketide synthase (PKS) gene cluster which was revealed when the genome was sequenced. The ca. 54-kb cluster contains three large genes, cpkA, cpkB and cpkC, encoding the PKS subunits. In silico analysis showed that the synthase consists of a loading module, five extension modules and a unique reductase as a terminal domain instead of a typical thioesterase. All acyltransferase domains are specific for a malonyl extender, and have a B-type ketoreductase. Tailoring and regulatory genes were also identified within the gene cluster. Surprisingly, some genes show high similarity to primary metabolite genes not commonly identified in any antibiotic biosynthesis cluster. Using western blot analysis with a PKS subunit (CpkC) antibody, CpkC was shown to be expressed in S. coelicolor at transition phase. Disruption of cpkC gave no obvious phenotype.