Nazzareno Dimasi

Human Natural Killer cell receptors: insights into their molecular function and structure

NK cells express receptors characterized by opposite functions that finely regulate their activities. Among inhibitory receptors, some are specific for different groups of MHC class I alleles, while others are still orphan receptors. On the contrary, various activating receptors are involved in the triggering of NK‐mediated natural cytotoxicity. In general, their engagement induces human NK cells to kill target cells that are either HLA class I‐negative or ‐deficient. Thus, the process of NK cell triggering mediated by Natural Cytotoxicity Receptors can be mainly considered as a non MHC‐restricted mechanism. Here, a brief description of the molecular nature of these receptors, as well as, of their 3D‐structures and of the implications for ligand recognition, is given.

Active Focal Segmental Glomerulosclerosis Is Associated with Massive Oxidation of Plasma Albumin

The basic mechanism for idiopathic FSGS still is obscure. Indirect evidence in humans and generation of FSGS by oxidants in experimental models suggest a role of free radicals. In vitro studies demonstrate a main role of plasma albumin as antioxidant, its modification representing a chemical marker of oxidative stress. With the use of complementary liquid chromatography electron spray ionization tandem mass spectrometry (LC-ESI-MS/MS) and biochemical methods, plasma albumin was characterized in 34 patients with FSGS; 18 had received a renal transplant, and 17 had IgM mesangial deposition. Patients with FSGS that was in remission or without recurrence after transplantation had normal plasma albumin, and the same occurred in patients with primary and secondary nephrites and with chronic renal failure. In contrast, patients with active FSGS or with posttransplantation recurrence had oxidized plasma albumin. This finding was based on the characterization of albumin Cys 34 with an mass-to-charge ratio of 511.71 in triple charge that was consistent with the formation of a cysteic acid carrying a sulfonic group (alb-SO(3)(-)). The exact mass of albumin was increased accordingly (+48 Da) for incorporation of three oxygen radicals. Direct titration of the free sulfhydryl group 34 of plasma albumin and electrophoretic titration curves confirmed loss of free sulfhydryl group and formation of a fast-moving isoform in all cases with disease activity. This is the first demonstration of in vivo plasma albumin oxidation that was obtained with an adequate structural approach. Albumin oxidation seems to be specific for FSGS, suggesting some pathogenetic implications. Free radical involvement in FSGS may lead to specific therapeutic interventions.

Critical Residues at the Ly49 Natural Killer Receptor’s Homodimer Interface Determine Functional Recognition of m157, a Mouse Cytomegalovirus MHC Class I-Like Protein

NK cell function is regulated by Ly49 receptors in mice and killer cell Ig-like receptors in humans. Although inhibitory Ly49 and killer cell Ig-like receptors predominantly ligate classical MHC class I molecules, recent studies suggest that their activating counterparts recognize infection. The quintessential example is resistance to the mouse CMV in C57BL/6 mice, which depends on the functional recognition of m157, a mouse CMV-encoded MHC class I-like molecule, by Ly49H, an activating NK cell receptor. We have taken advantage of the natural variation in closely related members of the Ly49C-like receptors and the availability of Ly49 crystal structures to understand the molecular determinants of the Ly49H-m157 interaction and to identify amino acid residues discriminating between m157 binding and nonbinding receptors. Using a site-directed mutagenesis approach, we have targeted residues conserved in receptors binding to m157 (Ly49H and Ly49I129) but different from receptors lacking m157 recognition (Ly49C, Ly49IB6, and Ly49U). Wild-type and mutant receptors were transfected into reporter cells, and physical binding as well as functional activation by m157 was studied. Our findings suggested that the Ly49 MHC class I contact “site 2,” I226, may not be involved in m157 binding. In contrast, residue Y146 and G151, mapping at the receptor homodimer interface, are likely critical for functional recognition of the m157 glycoprotein. Our combined functional and three-dimensional modeling approach suggested that the architecture of the Ly49H dimer is crucial to accessing m157, but not MHC class I. These results link Ly49 homodimerization variability to the direct recognition of pathogen products.

Identification and molecular modelling of a novel familial mutation in the SRY gene implicated in the pure gonadal dysgenesis

SRY gene is responsible for initiating male sexual differentiation. The protein encoded by SRY contains a homeobox (HMG) domain, which is a DNA-binding domain. Mutations of the SRY gene are reported to be associated with XY pure gonadal dysgenesis. The majority of these are de novo mutations affecting only one individual in a family. Only a small subset of mutations is shared between the father and one or more of his children. Most of these familial mutations are localized within the HMG box and only two are at the N-terminal domain of the SRY protein. Herein, we describe a young girl with pure gonadal dysgenesis and her father carrying a novel familial mutation in the SRY gene at codon number 3. This mutation is resulting in a serine (S) to leucine (L) substitution. The secondary structure of the SRY protein was carried out by protein modelling studies. This analysis suggests, with high possibility, that the N-terminal domain of the SRY protein, where we found the mutation, could form an α-helix from amino acid in position 2 to amino acid in position 13. The secondary structure prediction and the chemical properties of serine to leucine substitution stands for a potential disruption of this N-terminal α-helix in the SRY protein. This mutation could have some role in impeding the normal function of the SRY protein.

Structure of the saccharide-binding domain of the human natural killer cell inhibitory receptor p75/AIRM1.

The high-resolution crystal structure of the functional N-terminal domain from the extracellular region of the human natural killer cell inhibitory receptor p75/AIRM1 or Siglec-7 has been determined at 1.45 A resolution; it was obtained from a crystal belonging to a primitive monoclinic space group, with unit-cell parameters a = 32.65, b = 49.72, c = 39.79 A, alpha = gamma = 90, beta = 113 degrees. The structure reported here belongs to a different space group than the previously described Siglec-7 structure and was obtained using a bacterial expression system. The structure unveils the fine structural requirements adopted by a natural killer cell inhibitory receptor of the Siglec family in target-cell recognition and binding.

Human natural killer cell receptor functions and their implication in diseases.

At any given time, a natural killer cell must commit to life or death. How does a natural killer cell decide on this demanding task? Of course, this life-threatening decision is primarily orchestrated at the cell surface by protein–protein interactions. Thus, natural killer cells are equipped with an array of receptors that are responsible for sending signals in order to activate or inhibit their cytolytic activity. The goal of this review is to provide a functional and structural overview on innate immunity cell surface receptors in humans, which emerging data implicate to play a relevant role in different diseases. Although extremely interesting, it must be considered that this issue is mainly based on genetic correlation and there are controversial published data that will need further study.

Expression, refolding and crystallizations of the Grb2-like (GADS) C-terminal SH3 domain complexed with a SLP-76 motif peptide.

The Grb2-like adaptor protein GADS is composed of an N-terminal SH3 domain, an SH2 domain, a proline-rich region and a C-terminal SH3 domain. GADS interacts through its C-terminal SH3 domain with the adaptor protein SLP-76, thus recruiting this protein and other associated molecules to the linker for activation of T-cell (LAT) protein. The DNA encoding the C-terminal SH3 domain of GADS (GADS-cSH3) was assembled synthetically using a recursive PCR technique and the protein was overexpressed in Escherichia coli, refolded and purified. Several crystals of this domain in complex with the SLP-76 peptide were obtained and characterized.

Innate immunity in self and infectious nonself recognition

This innate immunity course was organized by the Ruggero Ceppellini Advanced School of Immunology [101], directed by Serafino Zappacosta, in collaboration with the Department of Cellular and Molecular Biology and Pathology of the University of Naples Federico II and the University of Catanzaro Medical School. The program was organized in to 13 lectures covering the role played by innate immunity in antimicrobial responses, the interplay and crosstalk of innate, and adaptive immune responses and how this information will influence the design of therapeutic protocols.