Publications

The binding of bacteria and platelets may play a central role in the pathogenesis of infective endocarditis. Platelet binding by Streptococcus gordonii strain M99 is predominantly mediated by the 286-kDa cell wall-anchored protein GspB. This unusually large protein lacks a typical amino-terminal signal peptide and is translocated from the cytoplasm via a dedicated transport system. A 14-kb segment just downstream of gspB encodes SecA2 and SecY2, two components of the GspB-specific transport system. The downstream segment also encodes several putative glycosyl transferases that may be responsible for the posttranslational modification of GspB. In this study, we compared the abilities of M99 and two GspB(-) mutant strains to bind various lectins. GspB was found to have affinity for lectins that bind N-acetylglucosamine. We also examined variant forms of GspB that lack a carboxy-terminal cell wall-anchoring domain and thus are free of covalent linkage to cell wall peptidoglycan. Like native GspB, these truncated proteins appear to be heavily glycosylated, as evidenced by migration during sodium dodecyl sulfate-polyacrylamide gel electrophoresis with an apparent molecular mass >100 kDa in excess of the predicted mass, negligible staining with conventional protein stains, and reactivity with hydrazide following periodate oxidation. Furthermore, analysis of the carbohydrate associated with the GspB variants by high-pH anion-exchange chromatography revealed the presence of approximately 70 to 100 monosaccharide residues per GspB polypeptide (primarily N-acetylglucosamine and glucose). Analysis of GspB in protoplasts of secA2 or secY2 mutant strains, which do not export GspB, indicates that GspB is glycosylated in the cytoplasm of these strains. The combined data suggest that the native GspB is a glycoprotein and that it may be glycosylated prior to export.

PURPOSE OF REVIEW

The prevalence of lipodystrophy in HIV infection reported in the early literature has varied widely due in part to the different methods used in assessing and defining lipodystrophy in studies. There remains a lack of clarity regarding whether the peripheral lipoatrophy and central lipohypertrophy initially described in HIV infection are a result of separate mechanisms or a single mechanism. We review the current methods used to assess and define lipodystrophy in HIV infection; the prevalence and incidence of lipodystrophy reported in the recent HIV literature; and future directions in elucidating the morphologic changes associated with HIV infection.

RECENT FINDINGS

Different methods of assessing and defining lipodystrophy continue to lead to varying prevalence and incidence rates in recent large cross-sectional and prospective studies. Recent studies that include a predominantly HIV-uninfected comparison group and utilize bi-directional surveys to describe fat loss and fat gain in both peripheral and central body sites suggest that there is an HIV-associated lipoatrophy that affects both peripheral and central sites. In one study that used objective measures to quantify fat such as magnetic resonance imaging, HIV-associated subcutaneous lipoatrophy appeared to predominate when compared with a healthy control group.

SUMMARY

Peripheral and central lipoatrophy affecting subcutaneous fat is emerging as the dominant morphologic change associated with HIV infection when compared with those without known HIV infection. Studies of lipodystrophy in HIV infection should focus on lipoatrophy using direct measures of fat when possible.

BACKGROUND

As a component of the innate immune system, natural killer (NK) cells may play a significant role in the early events after solid-organ transplantation. Activated NK cells have been shown to infiltrate allografts in transplant models. To better understand NK cells and the role of NK cell receptors in transplantation, we have cloned and begun characterizing a novel rat molecule, rNKp30.

METHODS

RNKp30 cDNA was cloned by 5' rapid amplification of cDNA ends polymerase chain reaction (PCR) and reverse transcriptase (RT)-PCR from mononuclear cells infiltrating a rejecting liver allograft. Southern blot analysis was used to determine the rNKp30 gene copy number. RT-PCR and Northern blotting were used to examine rNKp30 RNA expression in NK cells, multiple tissues, and liver grafts. Immunocytochemistry, immunoprecipitation, and Western blot analysis with two anti-rNKp30 polyclonal antibodies, CA680 and CA1071, were performed. Tunicamycin and endoglycosidase treatments determined the extent of rNKp30 glycosylation.

RESULTS

RNKp30 is homologous to human and macaque NKp30. It is a single copy gene with five identified single-nucleotide polymorphisms. RNKp30 is expressed by NK cells and is detectable as a single transcript by Northern blot in normal spleen, lymph node, and lung tissues. RNKp30 is a variably N-glycosylated cell surface molecule with a protein backbone of approximately 21 kDa. Elevated transcript expression of rNKp30 is detected in both rejected and spontaneously accepted liver allografts, but not in syngeneic or cyclosporine A-treated allografts.

CONCLUSIONS

RNKp30 is a glycosylated surface NK cell receptor with limited polymorphism. This putative activation receptor is expressed in liver allografts and may participate in the innate immune response after transplantation.

BACKGROUND

Patients with HIV infection exhibit increased rates of coronary events; however, the clinical features of acute coronary syndromes (ACS) in HIV-infected patients have not been well defined.

METHODS AND RESULTS

Between 1993 and 2003, 68 HIV-infected patients were hospitalized with ACS. We compared the clinical features and outcome of these patients with those of 68 randomly selected control patients with ACS without HIV. HIV patients were on average more than a decade younger than controls and more likely to be male and current smokers and to have low HDL cholesterol. They were less likely than controls to have diabetes or hyperlipidemia, and their TIMI (Thrombolysis In Myocardial Infarction) risk scores on admission were significantly lower. At coronary angiography, the number of vessels with >50% stenosis was 1.3+/-1.0 in HIV patients and 1.9+/-1.2 in controls (P=0.007). Restenosis developed in 15 of 29 HIV patients who underwent percutaneous coronary intervention compared with 3 of 21 controls (52% versus 14%, P=0.006).

CONCLUSIONS

HIV patients with ACS are younger and more likely to be males and current smokers and to have low HDL cholesterol levels compared with other ACS patients. Their TIMI risk scores are lower, and they are more likely to have single-vessel disease; however, their restenosis rates after percutaneous coronary intervention are unexpectedly high.

Two main entry points for electrons into the mitochondrial respiratory chain are NADH:ubiquinone oxidoreductase (complex I) and succinate:ubiquinone oxidoreductase (complex II). Metabolic regulation of these two respiratory complexes is not understood in detail. It has been suggested that the Krebs cycle metabolic intermediate oxaloacetate (OAA) inhibits complex II in vivo, whereas complex I undergoes a reversible active/de-active transition. In normoxic and anoxic hearts it has been shown that the proportion of complex I in the active and de-active states is different suggesting a possible mode of regulation of the enzyme by oxygen concentration. In the current studies rapid isolation of mitochondrial membranes in a state that preserves the activity of both complex I and complex II has been achieved using Langendorff perfused rat hearts. The findings indicate that the state of activation of complex I is controlled by the oxygen saturation in the perfusate. In addition, these studies show that complex II is fully active in the mitochondrion and not inhibited by OAA regardless of the oxygen concentration.