The crystal structure of the varicella-zoster Orf24-Orf27 nuclear egress complex spotlights multiple determinants of herpesvirus subfamily specificity.

Varicella-zoster virus (VZV) is a human pathogen from the α-subfamily of herpesviruses. The VZV Orf24-Orf27 complex represents the essential viral core nuclear egress complex (NEC) that orchestrates the egress of the preassembled virus capsids from the nucleus. While previous studies have primarily emphasized that the architecture of core NEC complexes is highly conserved among herpesviruses, the present report focuses on subfamily-specific structural and functional features that help explain the differences in the autologous versus nonautologous interaction patterns observed for NEC formation across herpesviruses.

High-resolution crystal structures of two prototypical β- and γ-herpesviral nuclear egress complexes unravel the determinants of subfamily specificity.

Herpesviruses uniquely express two essential nuclear egress-regulating proteins forming a heterodimeric basic structure of the nuclear egress complex (core NEC). These core NECs serve as a hexameric lattice-structured platform for capsid docking and recruit viral and cellular NEC-associated factors that jointly exert nuclear lamina- and membrane-rearranging functions (multicomponent NEC). Here, we report the X-ray structures of β- and γ-herpesvirus core NECs obtained through an innovative recombinant expression strategy based on NEC-hook::NEC-groove protein fusion constructs.

Structural and functional characterization of SiiA, an auxiliary protein from the SPI4-encoded type 1 secretion system from Salmonella enterica.

Salmonella invasion is mediated by a concerted action of the Salmonella pathogenicity island 4 (SPI4)-encoded type one secretion system (T1SS) and the SPI1-encoded type three secretion system (T3SS-1). The SPI4-encoded T1SS consists of five proteins (SiiABCDF) and secretes the giant adhesin SiiE. Here, we investigated structure-function relationships in SiiA, a non-canonical T1SS subunit.

PRISEs (progesterone 5β-reductase and/or iridoid synthase-like 1,4-enone reductases): Catalytic and substrate promiscuity allows for realization of multiple pathways in plant metabolism.

PRISEs (progesterone 5β-reductase and/or iridoid synthase-like 1,4-enone reductases) are involved in cardenolide and iridoid biosynthesis. We here investigated a PRISE (rAtSt5βR) from Arabidopsis thaliana, a plant producing neither cardenolides nor iridoids. The structure of rAtSt5βR was elucidated with X-ray crystallography and compared to the known structures of PRISEs from Catharanthus roseus (rCrISY) and Digitalis lanata (rDlP5βR).

Crystal Structure of the Extracellular Domain of the Human Dendritic Cell Surface Marker CD83.

CD83 is a type-I membrane protein and an efficient marker for identifying mature dendritic cells. Whereas membrane-bound, full-length CD83 co-stimulates the immune system, a soluble variant (sCD83), consisting of the extracellular domain only, displays strong immune-suppressive activities. Besides a prediction that sCD83 adopts a V-set Ig-like fold, however, little is known about the molecular architecture of CD83 and the mechanism by which CD83 exerts its function on dendritic cells and additional immune cells.

Expression, crystallization and structure elucidation of γ-terpinene synthase from Thymus vulgaris.

The biosynthesis of γ-terpinene, a precursor of the phenolic isomers thymol and carvacrol found in the essential oil from Thymus sp., is attributed to the activitiy of γ-terpinene synthase (TPS). Purified γ-terpinene synthase from T.

Crystal Structure of the Human Cytomegalovirus pUL50-pUL53 Core Nuclear Egress Complex Provides Insight into a Unique Assembly Scaffold for Virus-Host Protein Interactions.

Nuclear replication of cytomegalovirus relies on elaborate mechanisms of nucleocytoplasmic egress of viral particles. Thus, the role of two essential and conserved viral nuclear egress proteins, pUL50 and pUL53, is pivotal. pUL50 and pUL53 heterodimerize and form a core nuclear egress complex (NEC), which is anchored to the inner nuclear membrane and provides a scaffold for the assembly of a multimeric viral-cellular NEC.

Endothelium-protective sphingosine-1-phosphate provided by HDL-associated apolipoprotein M.

Protection of the endothelium is provided by circulating sphingosine-1-phosphate (S1P), which maintains vascular integrity. We show that HDL-associated S1P is bound specifically to both human and murine apolipoprotein M (apoM). Thus, isolated human ApoM(+) HDL contained S1P, whereas ApoM(-) HDL did not.

Serendipitous fatty acid binding reveals the structural determinants for ligand recognition in apolipoprotein M.

Apolipoprotein M (ApoM) is a 25-kDa HDL-associated apolipoprotein and a member of the lipocalin family of proteins. Mature apoM retains its signal peptide, which serves as a lipid anchor attaching apoM to the lipoproteins, thereby keeping it in the circulation. Studies in mice have suggested apoM to be antiatherogenic, but its physiological function is yet unknown.

A protein functional leap: how a single mutation reverses the function of the transcription regulator TetR.

Today's proteome is the result of innumerous gene duplication, mutagenesis, drift and selection processes. Whereas random mutagenesis introduces predominantly only gradual changes in protein function, a case can be made that an abrupt switch in function caused by single amino acid substitutions will not only considerably further evolution but might constitute a prerequisite for the appearance of novel functionalities for which no promiscuous protein intermediates can be envisaged. Recently, tetracycline repressor (TetR) variants were identified in which binding of tetracycline triggers the repressor to associate with and not to dissociate from the operator DNA as in wild-type TetR.

The crystal structure of progesterone 5beta-reductase from Digitalis lanata defines a novel class of short chain dehydrogenases/reductases.

Progesterone 5beta-reductase (5beta-POR) catalyzes the stereospecific reduction of progesterone to 5beta-pregnane-3,20-dione and is a key enzyme in the biosynthetic pathway of cardenolides in Digitalis (foxglove) plants. Sequence considerations suggested that 5beta-POR is a member of the short chain dehydrogenase/reductase (SDR) family of proteins but at the same time revealed that the sequence motifs that in standard SDRs contain the catalytically important residues are missing. Here we present crystal structures of 5beta-POR from Digitalis lanata in complex with NADP(+) at 2.

Crystal structure analysis and solution studies of human Lck-SH3; zinc-induced homodimerization competes with the binding of proline-rich motifs.

In cytosolic Src-type tyrosine kinases the Src-type homology 3 (SH3) domain binds to an internal proline-rich motif and the presence or the absence of this interaction modulates the kinase enzymatic activity. The Src-type kinase Lck plays an important role during T-cell activation and development, since it phosphorylates the T-cell antigen receptor in an early step of the activation pathway. We have determined the crystal structure of the SH3 domain from Lck kinase at a near-atomic resolution of 1.

Crystallization and preliminary crystallographic analysis of selenomethionine-labelled progesterone 5beta-reductase from Digitalis lanata Ehrh.

Progesterone 5beta-reductase (5beta-POR) catalyzes the reduction of progesterone to 5beta-pregnane-3,20-dione and is the first stereospecific enzyme in the putative biosynthetic pathway of Digitalis cardenolides. Selenomethionine-derivatized 5beta-POR from D. lanata was successfully overproduced and crystallized.