HIV-1 p6-Another viral interaction partner to the host cellular protein cyclophilin A.

The 52-amino acid human immunodeficiency virus type 1 (HIV-1) p6 protein has previously been recognized as a docking site for several cellular and viral binding factors and is important for the formation of infectious viruses. A particular structural feature of p6 is the notably high relative content of proline residues, located at positions 5, 7, 10, 11, 24, 30, 37 and 49 in the sequence. Proline cis/trans isomerism was detected for all these proline residues to such an extent that more than 40% of all p6 molecules contain at least one proline in a cis conformation. 2D (1)H nuclear magnetic resonance analysis of full-length HIV-1 p6 and p6 peptides established that cyclophilin A (CypA) interacts as a peptidyl-prolyl cis/trans isomerase with all proline residues of p6. Only catalytic amounts of CypA were necessary for the interaction with p6 to occur, strongly suggesting that the observed interaction is highly relevant in vivo. In addition, surface plasmon resonance studies revealed binding of full-length p6 to CypA, and that this binding was significantly stronger than any of its N- or C-terminal peptides. This study demonstrates the first identification of an interaction between HIV-1 p6 and the host cellular protein CypA. The mode of interaction involves both transient enzyme-substrate interactions and a more stable binding. The binding motifs of p6 to Tsg-101, ALIX and Vpr coincide with binding regions and catalytic sites of p6 to CypA, suggesting a potential role of CypA in modulating functional interactions of HIV-1.

The intriguing cyclophilin A-HIV-1 Vpr interaction: prolyl cis/trans isomerisation catalysis and specific binding.

BACKGROUND: Cyclophilin A (CypA) represents a potential target for antiretroviral therapy since inhibition of CypA suppresses human immunodeficiency virus type 1 (HIV-1) replication, although the mechanism through which CypA modulates HIV-1 infectivity still remains unclear. The interaction of HIV-1 viral protein R (Vpr) with the human peptidyl prolyl isomerase CypA is known to occur in vitro and in vivo. However, the nature of the interaction of CypA with Pro-35 of N-terminal Vpr has remained undefined. RESULTS: Characterization of the interactions of human CypA with N-terminal peptides of HIV-1 Vpr has been achieved using a combination of nuclear magnetic resonace (NMR) exchange spectroscopy and surface plasmon resonance spectroscopy (SPR). NMR data at atomic resolution indicate prolyl cis/trans isomerisation of the highly conserved proline residues Pro-5, -10, -14 and -35 of Vpr are catalyzed by human CypA and require only very low concentrations of the isomerase relative to that of the peptide substrates. Of the N-terminal peptides of Vpr only those containing Pro-35 bind to CypA in a biosensor assay. SPR studies of specific N-terminal peptides with decreasing numbers of residues revealed that a seven-residue motif centred at Pro-35 consisting of RHFPRIW, which under membrane-like solution conditions comprises the loop region connecting helix 1 and 2 of Vpr and the two terminal residues of helix 1, is sufficient to maintain strong specific binding. CONCLUSIONS: Only N-terminal peptides of Vpr containing Pro-35, which appears to be vital for manifold functions of Vpr, bind to CypA in a biosensor assay. This indicates that Pro-35 is essential for a specific CypA-Vpr binding interaction, in contrast to the general prolyl cis/trans isomerisation observed for all proline residues of Vpr, which only involve transient enzyme-substrate interactions. Previously suggested models depicting CypA as a chaperone that plays a role in HIV-1 virulence are now supported by our data. In detail the SPR data of this interaction were compatible with a two-state binding interaction model that involves a conformational change during binding. This is in accord with the structural changes observed by NMR suggesting CypA catalyzes the prolyl cis/trans interconversion during binding to the RHFP35RIW motif of N-terminal Vpr.

Cytokine and autoantibody profiling related to histopathological features in primary Sjogren's syndrome.

OBJECTIVE: To investigate a potential correlation between circulating cytokine and autoantibody levels and histopathological features in subgroups of patients with primary SS (pSS). METHODS: Minor salivary gland biopsies from a cohort of 141 patients fulfilling the American-European consensus classification criteria for pSS were re-examined and grouped according to focus score (FS) and germinal centre (GC) status; serum samples were analysed for autoantibodies, chemokines and cytokines. RESULTS: Of the 115 available biopsies, 18 (16%) lacked characteristic focal mononuclear cell infiltrates [FS < 1 (FS-)] but patients were positive for Ro/SSA and/or La/SSB. IL-17, IL-1RA, IL-15, macrophage inflammatory protein (MIP)-1alpha, MIP-1beta, eotaxin, IFN-alpha and IL-4 levels were significantly increased in the 27 (23%) patients with ectopic GC formation (GC+) in the salivary glands compared with the GC- patients (n = 70). In addition, minor differences in cytokine levels were found when comparing age groups. CONCLUSION: Degenerative changes observed in the minor salivary glands of patients with pSS may represent 'burned out' inflammation. The elevated levels of IL-4 found in these patients may influence the reduced salivary flow observed in GC+ patients. Increased titres of Th17-associated cytokines, IL-17, IL-1beta and the IL-23 subunit IL-12p40, may indicate a higher activity of these cells in GC+ patients. Differences in cytokine levels may be utilized when sub-grouping the SS patients into disease phases and may consequently have implications for treatment.

Sjögren's syndrome: an update on epidemiology and current insights on pathophysiology.

Primary Sjögren's syndrome (pSS) is an autoimmune chronic inflammatory disorder affecting 0.2% to 3.0% of the population, with a 9:1 female to male ratio. Features are oral and ocular dryness, local and systemic autoantibody production, and progressive focal mononuclear cell infiltration in the affected salivary and lacrimal glands. Lymphoma is the most severe complication of pSS, occurring in 4% to 5% of patients. Genetic studies identified an association with HLA and susceptibility genes in cytokine genes and genes involved in B-cell differentiation. Genetic variations may help explain why disease manifestations differ among patients and supports the hypothesis of certain distinct disease phenotypes.