Complement factor 5a receptor chimeras reveal the importance of lipid-facing residues in transport competence

Severe neutropenia in patients with chronic hepatitis C: a benign condition

BACKGROUND/AIMS

Patients with chronic hepatitis C virus (HCV) infection may develop neutropenia, which can delay or prevent treatment. Severe neutropenia, absolute neutrophil counts (ANC) ≤0.500 × 10(9)/l, is a rare finding, with only two isolated reports published in the literature. The aim of this study was to evaluate the incidence and natural history of severe neutropenia in hepatitis C patients.

METHODS

The records of 685 patients with active HCV were reviewed to identify those with severe neutropenia. The laboratory parameters and clinical history data of patients with severe neutropenia were then compared to a cohort of patients with HCV patients who had the more common minor neutropenia (ANC = 1.000-1.500 10(9)/l).

RESULTS

There was no significant difference in race, MELD (Model for End Stage Liver Disease) scores, portal hypertension, splenomegaly, viral load, viral type, or hemoglobin or platelet levels. Neither group suffered serious systemic infections.

CONCLUSIONS

Severe neutropenia in HCV patients is underreported and not associated with serious HCV complications such as elevated MELD score or cirrhosis. Serious infection is rare and patients respond well to granulocyte colony-stimulating factor. Severely neutropenic patients with HCV appear to have a benign course and may be candidates for antiviral therapy.

Structural basis of M3 muscarinic receptor dimer/oligomer formation

Class A G protein-coupled receptors (GPCRs) are known to form dimers and/or oligomeric arrays in vitro and in vivo. These complexes are thought to play important roles in modulating class A GPCR function. Many studies suggest that residues located on the "outer" (lipid-facing) surface of the transmembrane (TM) receptor core are critically involved in the formation of class A receptor dimers (oligomers). However, no clear consensus has emerged regarding the identity of the TM helices or TM subsegments involved in this process. To shed light on this issue, we have used the M(3) muscarinic acetylcholine receptor (M3R), a prototypic class A GPCR, as a model system. Using a comprehensive and unbiased approach, we subjected all outward-facing residues (70 amino acids total) of the TM helical bundle (TM1-7) of the M3R to systematic alanine substitution mutagenesis. We then characterized the resulting mutant receptors in radioligand binding and functional studies and determined their ability to form dimers (oligomers) in bioluminescence resonance energy transfer saturation assays. We found that M3R/M3R interactions are not dependent on the presence of one specific structural motif but involve the outer surfaces of multiple TM subsegments (TM1-5 and -7) located within the central and endofacial portions of the TM receptor core. Moreover, we demonstrated that the outward-facing surfaces of most TM helices play critical roles in proper receptor folding and/or function. Guided by the bioluminescence resonance energy transfer data, molecular modeling studies suggested the existence of multiple dimeric/oligomeric M3R arrangements, which may exist in a dynamic equilibrium. Given the high structural homology found among all class A GPCRs, our results should be of considerable general relevance.