ABSTRACT
BACKGROUND: Polyketides are structurally diverse natural products that have a range of medically useful activities. Nonaromatic bacterial polyketides are synthesised on modular polyketide synthase (PKS) multienzymes, in which each cycle of chain extension requires a different 'module' of enzymatic activities. Attempts to design and construct modular PKSs that synthesise specified novel polyketides provide a particularly stringent test of our understanding of PKS structure and function. RESULTS: We have constructed bimodular and trimodular PKSs based on DEBS1-TE, a derivative of the erythromycin PKS that contains only modules 1 and 2 and a thioesterase (TE), by substituting multiple domains with appropriate counterparts derived from the rapamycin PKS. Hybrid PKSs were obtained that synthesised the predicted target triketide lactones, which are simple analogues of cholesterol-lowering statins. In constructing intermodular fusions, whether between modules in the same or in different proteins, it was found advantageous to preserve intact the acyl carrier protein-ketosynthase (ACP-KS) didomain that spans the junction between successive modules. CONCLUSIONS: Relatively simple considerations govern the construction of functional hybrid PKSs. Fusion sites should be chosen either in the surface-accessible linker regions between enzymatic domains, as previously revealed, or just inside the conserved margins of domains. The interaction of an ACP domain with the adjacent KS domain, whether on the same polyketide or not, is of particular importance, both through conservation of appropriate protein-protein interactions, and through optimising molecular recognition of the altered polyketide chain in the key transfer of the acyl chain from the ACP of one module to the KS of the downstream module.
Subject(s)
Drug Design , Multienzyme Complexes/chemistry , Protein Engineering , Amino Acid Sequence , Hypolipidemic Agents/chemistry , Lactones , Models, Chemical , Models, Molecular , Molecular Sequence Data , Multienzyme Complexes/genetics , Protein Conformation , SaccharopolysporaABSTRACT
A case of cholesterol embolisation (CE) following instrumentation of an aneurysmal aorta is presented. The patient developed myalgias, livedo reticularis in the buttocks, suprapubic area and legs, that progressed to patchy gangrene and renal failure. Maximum conservative management including heparin, iloprost and haemodialysis was ineffective, in keeping with previous reports that there is no known therapy for CE. The aetiology, presentation, treatment and prognosis of this condition is discussed. With the ever increasing use of endovascular treatment of abdominal aortic aneurysms, this complication may be more frequently encountered.
Subject(s)
Aortic Aneurysm, Abdominal/complications , Embolism, Cholesterol/etiology , Postoperative Complications/etiology , Aged , Aortic Aneurysm, Abdominal/pathology , Aortic Aneurysm, Abdominal/surgery , Buttocks , Embolism, Cholesterol/pathology , Fatal Outcome , Female , Gangrene , Humans , Multiple Organ Failure/etiology , Multiple Organ Failure/pathology , Postoperative Complications/pathologyABSTRACT
The amino acid sequences of a large number of polyketide synthase domains that catalyse the transacylation of either methylmalonyl-CoA or malonyl-CoA onto acyl carrier protein (ACP) have been compared. Regions were identified in which the acyltransferase sequences diverged according to whether they were specific for malonyl-CoA or methylmalonyl-CoA. These differences are sufficiently clear to allow unambiguous assignment of newly-sequenced acyltransferase domains in modular polyketide synthases. Comparison with the recently-determined structure of the malonyltransferase from Escherichia coli fatty acid synthase showed that the divergent region thus identified lies near the acyltransferase active site, though not close enough to make direct contact with bound substrate.
Subject(s)
Acyltransferases/chemistry , Multienzyme Complexes/chemistry , Acyl Carrier Protein/metabolism , Acyl-Carrier Protein S-Malonyltransferase , Acyltransferases/metabolism , Amino Acid Sequence , Binding Sites , Consensus Sequence , Malonyl Coenzyme A/metabolism , Molecular Sequence Data , Multienzyme Complexes/metabolism , Sequence Homology, Amino Acid , Substrate SpecificityABSTRACT
This study examined the records of 218 patients from the 5-year period 1979-1983 who were treated for palatally ectopic canines in the Glasgow Dental Hospital. It tested the hypothesis that there was a relationship between the age of the patient at diagnosis, and the complexity and outcome of treatment. Whilst the age of the patient had no influence on the complexity of the treatment required, it had a significant effect on the outcome since it was related to the number of failed appointments and the likelihood of completing treatment successfully.
