Design of Industrial Standards for the Calibration of Optical Microscopes.

One of the most important fields of study in material science is surface characterization. This topic is currently a field of growing interest as many functional properties depend on the surface texture. In this paper the authors, after a short a review of different methods for surface topography characterization and the determination of the traceability problems that arise in this type of measurements, propose four different designs of material standards that can be used to calibrate the most common optical measuring instruments used for these tasks, such as measuring microscopes, metallurgical microscopes, confocal microscopes, focus variation microscopes, etc.

Fates of retroviral core components during unrestricted and TRIM5-restricted infection.

TRIM5 proteins can restrict retroviral infection soon after delivery of the viral core into the cytoplasm. However, the molecular mechanisms by which TRIM5α inhibits infection have been elusive, in part due to the difficulty of developing and executing biochemical assays that examine this stage of the retroviral life cycle. Prevailing models suggest that TRIM5α causes premature disassembly of retroviral capsids and/or degradation of capsids by proteasomes, but whether one of these events leads to the other is unclear.

Tetherin inhibits HIV-1 release by directly tethering virions to cells.

Tetherin is an interferon-induced protein whose expression blocks the release of HIV-1 and other enveloped viral particles. The underlying mechanism by which tetherin functions and whether it directly or indirectly causes virion retention are unknown. Here, we elucidate the mechanism by which tetherin exerts its antiviral activity.

Evidence for restriction of ancient primate gammaretroviruses by APOBEC3 but not TRIM5alpha proteins.

Because of evolutionary pressures imposed through episodic colonization by retroviruses, many mammals express factors, such as TRIM5alpha and APOBEC3 proteins, that directly restrict retroviral replication. TRIM5 and APOBEC restriction factors are most often studied in the context of modern primate lentiviruses, but it is likely that ancient retroviruses imposed the selective pressure that is evident in primate TRIM5 and APOBEC3 genes. Moreover, these antiretroviral factors have been shown to act against a variety of retroviruses, including gammaretroviruses.

Membrane cofactor protein (MCP, CD46) binding to clinical isolates of Streptococcus pyogenes: binding to M type 18 strains is independent of Emm or Enn proteins.

The complement regulatory protein CD46 (MCP, membrane cofactor protein) is used as a cell receptor by a number of bacterial and viral pathogens, including Streptococcus pyogenes (Group A Streptococci). The highly variable M (Emm) proteins are virulence factors of S. pyogenes, and Emm proteins of serotypes 5, 6 or 22 are able of binding to CD46, thus mediating the binding of Streptococci to human cells.

Antiretroviral potential of human tripartite motif-5 and related proteins.

TRIM5alpha is a potent inhibitor of infection by diverse retroviruses and is encoded by one of a large family of TRIM genes. We found that several TRIM motifs among a panel of selected human TRIM proteins (TRIM1, 5, 6, 18, 19, 21 22, 34) could inhibit infection when artificially targeted to an incoming HIV-1 capsid. Conversely, when ectopically expressed as authentic full-length proteins, most lacked activity against a panel of retroviruses.

Restriction of human immunodeficiency virus type 1 by TRIM-CypA occurs with rapid kinetics and independently of cytoplasmic bodies, ubiquitin, and proteasome activity.

TRIM-CypA is an owl monkey-specific variant of the retrovirus restriction factor TRIM5alpha. Here, we exploit its modular domain organization and cyclosporine sensitivity to probe the kinetics and mechanism of TRIM5-mediated restriction. Time of addition/withdrawal experiments reveal that inhibition of incoming human immunodeficiency virus type 1 capsids by TRIM-CypA occurs within minutes of their delivery to the target cell cytoplasm.

Human tripartite motif 5alpha domains responsible for retrovirus restriction activity and specificity.

The tripartite motif 5alpha protein (TRIM5alpha) is one of several factors expressed by mammalian cells that inhibit retrovirus replication. Human TRIM5alpha (huTRIM5alpha) inhibits infection by N-tropic murine leukemia virus (N-MLV) but is inactive against human immunodeficiency virus type 1 (HIV-1). However, we show that replacement of a small segment in the carboxy-terminal B30.

Cyclophilin interactions with incoming human immunodeficiency virus type 1 capsids with opposing effects on infectivity in human cells.

Cyclophilin A (CypA) is a peptidyl-prolyl isomerase that binds to the capsid protein (CA) of human immunodeficiency virus type 1 (HIV-1) and by doing so facilitates HIV-1 replication. Although CypA is incorporated into HIV-1 virions by virtue of CypA-Gag interactions that occur during virion assembly, in this study we show that the CypA-CA interaction that occurs following the entry of the viral capsid into target cells is the major determinant of CypA's effects on HIV-1 replication. Specifically, by using normal and CypA-deficient Jurkat cells, we demonstrate that the presence of CypA in the target and not the virus-producing cell enhances HIV-1 infectivity.

Interaction between complement regulators and Streptococcus pyogenes: binding of C4b-binding protein and factor H/factor H-like protein 1 to M18 strains involves two different cell surface molecules.

Streptococcus pyogenes, or group A Streptococcus, is one of the most frequent causes of pharyngitis and skin infections in humans. Many virulence mechanisms have been suggested to be involved in the infectious process. Among them is the binding to the bacterial cell surface of the complement regulatory proteins factor H, factor H-like protein 1 (FHL-1), and C4b-binding protein.

APOBEC3G incorporation into human immunodeficiency virus type 1 particles.

APOBEC3G is promiscuous with respect to its antiretroviral effect, requiring that it be packaged into diverse retrovirus particles. Here, we show that most virally encoded human immunodeficiency virus type 1 particle components are dispensable for APOPEC3G incorporation. However, replacement of the nucleocapsid (NC) Gag domain with a leucine zipper abolished APOBEC3G incorporation.

Human immunodeficiency virus type 1 matrix inhibits and confers cooperativity on gag precursor-membrane interactions.

Human immunodeficiency virus type 1 (HIV-1) Gag multimerization and membrane binding are required for particle formation. However, it is unclear what constitutes a minimal plasma membrane-specific targeting signal and what role the matrix (MA) globular head and other Gag domains play in membrane targeting. Here, we use membrane flotation and microscopic analysis of Gag deletion mutants to demonstrate that the HIV-1 MA globular head inhibits a plasma membrane-specific targeting signal contained within the six amino-terminal MA residues.

Retrovirus resistance factors Ref1 and Lv1 are species-specific variants of TRIM5alpha.

Mammalian cells express several factors that act in a cell-autonomous manner to inhibit retrovirus replication. Among these are the Friend virus susceptibility factor 1/lentivirus susceptibility factor 1/restriction factor 1 (Ref1) class of restriction factors, which block infection by targeting the capsids of diverse retroviruses. Here we show that lentivirus susceptibility factor 1 and Ref1 are species-specific variants of tripartite interaction motif 5alpha (TRIM5alpha), a cytoplasmic body component recently shown to block HIV-1 infection in rhesus macaque cells, and can indeed block infection by widely divergent retroviruses.

Context-dependent effects of L domains and ubiquitination on viral budding.

Many enveloped viruses encode late assembly domains, or L domains, that facilitate virion egress. PTAP-type L domains act by recruiting the ESCRT-I (endosomal sorting complex required for transport I) component Tsg101, and YPXL/LXXLF-type L domains recruit AIP-1/ALIX, both of which are class E vacuolar protein sorting (VPS) factors, normally required for the generation of vesicles within endosomes. The binding cofactors for PPXY-type L domains have not been unambiguously resolved but may include Nedd4-like ubiquitin ligases.

Divergent retroviral late-budding domains recruit vacuolar protein sorting factors by using alternative adaptor proteins.

The release of enveloped viruses from infected cells often requires a virally encoded activity, termed a late-budding domain (L domain), encoded by essential PTAP, PPXY, or YPDL sequence motifs. PTAP-type L domains recruit one of three endosomal sorting complexes required for transport (ESCRT-I). However, subsequent events in viral budding are poorly defined, and neither YPDL nor PPXY-type L domains require ESCRT-I.

Structural and functional characterization of factor H mutations associated with atypical hemolytic uremic syndrome.

Genetic studies have demonstrated the involvement of the complement regulator factor H in nondiarrheal, nonverocytotoxin (i.e., atypical) cases of hemolytic uremic syndrome.