Biomedical subjects

Jay I Koepke

Publications and source records attributed to Jay I Koepke.

4 recordsLinked to original sources

PubMed2006

Peroxisomes and aging.

Peroxisomes are indispensable for proper functioning of human cells. They efficiently compartmentalize enzymes responsible for a number of metabolic processes, including the absolutely essential beta-oxidation of specific fatty acid chains. These and other oxidative reactions produce hydrogen peroxide, which is, in most instances, immediately processed in situ to water and oxygen. The responsible peroxidase is the heme-containing tetrameric enzyme, catalase. What has emerged in recent years is that there are circumstances in which the tightly regulated balance of hydrogen peroxide producing and degrading activities in peroxisomes is upset-leading to the net production and accumulation of hydrogen peroxide and downstream reactive oxygen species. The factor most essentially involved is catalase, which is missorted in aging, missing or present at reduced levels in certain disease states, and inactivated in response to exposure to specific xenobiotics. The overall goal of this review is to summarize the molecular events associated with the development and advancement of peroxisomal hypocatalasemia and to describe its effects on cells. In addition, results of recent efforts to increase levels of peroxisomal catalase and restore oxidative balance in cells will be discussed.

Acatalasia↗

PubMed2006

Hypocatalasemic fibroblasts accumulate hydrogen peroxide and display age-associated pathologies.

Human epidemiological studies point to an association of hypocatalasemia and an increased risk of age-related disease. Unfortunately, the cellular and molecular manifestations of hypocatalasemia are only poorly understood. In this analysis, we have extensively characterized hypocatalasemic human fibroblasts and report that they amass hydrogen peroxide and are oxidatively damaged. Protein and DNA alike are affected, as are functioning and biogenesis of peroxisomes - the subcellular organelles which normally house catalase. Despite these pathologies and their relative inability to grow, the cells do not appear to be intrinsically senescent. With the goal of restoring oxidative balance and perhaps reversing some of the accumulated damage to critical cellular components, we transduced hypocatalasemic fibroblasts with a form of catalase specifically designed to efficiently traffic to peroxisomes. We show the strategy is extremely effective, with dramatic reductions seen in cellular hydrogen peroxide levels. Future longitudinal studies aimed at examining the effects of a more continuous and long-term protein therapy may now commence.

Age Factors↗

PubMed2004

Crystal structures of a multidrug-resistant human immunodeficiency virus type 1 protease reveal an expanded active-site cavity.

The goal of this study was to use X-ray crystallography to investigate the structural basis of resistance to human immunodeficiency virus type 1 (HIV-1) protease inhibitors. We overexpressed, purified, and crystallized a multidrug-resistant (MDR) HIV-1 protease enzyme derived from a patient failing on several protease inhibitor-containing regimens. This HIV-1 variant contained codon mutations at positions 10, 36, 46, 54, 63, 71, 82, 84, and 90 that confer drug resistance to protease inhibitors. The 1.8-angstrom (A) crystal structure of this MDR patient isolate reveals an expanded active-site cavity. The active-site expansion includes position 82 and 84 mutations due to the alterations in the amino acid side chains from longer to shorter (e.g., V82A and I84V). The MDR isolate 769 protease "flaps" stay open wider, and the difference in the flap tip distances in the MDR 769 variant is 12 A. The MDR 769 protease crystal complexes with lopinavir and DMP450 reveal completely different binding modes. The network of interactions between the ligands and the MDR 769 protease is completely different from that seen with the wild-type protease-ligand complexes. The water molecule-forming hydrogen bonds bridging between the two flaps and either the substrate or the peptide-based inhibitor are lacking in the MDR 769 clinical isolate. The S1, S1', S3, and S3' pockets show expansion and conformational change. Surface plasmon resonance measurements with the MDR 769 protease indicate higher k(off) rates, resulting in a change of binding affinity. Surface plasmon resonance measurements provide k(on) and k(off) data (K(d) = k(off)/k(on)) to measure binding of the multidrug-resistant protease to various ligands. This MDR 769 protease represents a new antiviral target, presenting the possibility of designing novel inhibitors with activity against the open and expanded protease forms.

Binding Sites↗

PubMed2002

Peroxisome senescence in human fibroblasts.

The molecular mechanisms of peroxisome biogenesis have begun to emerge; in contrast, relatively little is known about how the organelle functions as cells age. In this report, we characterize age-related changes in peroxisomes of human cells. We show that aging compromises peroxisomal targeting signal 1 (PTS1) protein import, affecting in particular the critical antioxidant enzyme catalase. The number and appearance of peroxisomes are altered in these cells, and the organelles accumulate the PTS1-import receptor, Pex5p, on their membranes. Concomitantly, cells produce increasing amounts of the toxic metabolite hydrogen peroxide, and we present evidence that this increased load of reactive oxygen species may further reduce peroxisomal protein import and exacerbate the effects of aging.

Aging↗