Antifungal Peptide Modeling, Folding and Mimetic Design

The antifungal peptides represent diverse structures for drug design. Unfortunately, they provide inferior drug candidates because of their low oral bioavailability, potential immunogenicity, poor in vivo metabolic stability and high molecular weight. Recent efforts have focused on the creation of non-natural peptide mimetics. Their artificial backbone makes most peptidomimetics resistant to degradative enzymes, thus, increasing the stability of peptidomimetic drugs in the body. In the present study, four antifungal peptidomimetics structures named C1 to C4 were designed based on the antifungal decapeptide crystallized structure of Pep-1 using bioinformatics tools. Structures C1 and C2 belong to the N-terminal part of Pep-1 and C3 and C4 belong to the C-terminal amino acid sequence part of Pep-1. Minimum inhibitory concentrations (MIC) of these structures were estimated against Aspergillus niger N402, Candida albicans ATCC 10231, and Saccharomyces cerevisiae PTCC 5052. Structures C2 and C1 showed more potent antifungal activities against these fungal strains compared to C3 and C4, respectively. This demonstrated that the N-terminal part is more potent for antifungal activity and indicated that the N-terminal part of antifungal peptides is more active and important for antifungal activity than the C-terminal. Structure C2 was demonstrated to be more active against these microorganisms and could be used as a potential target for future antifungal peptidomimetics studies. Important factors/descriptors of 63 antifungal peptides have been studied using Artificial Neural Network (ANN). The most important factors determined were amino acid number 1 (S1), Log P, and their α-helix contents. This is the first study on the structure of C1 to C4 peptidomimetics on Aspergillus niger N402, Candida albicans ATCC 10231, and Saccharomyces cerevisiae PTCC 5052

Interaction of Hsp104 with Hsp70: Insight into the Mechanism of Protein Disaggregation

Hsp104 and ClpB are hexameric ATPases that resolubilize aggregated proteins in collaboration with the Hsp70 chaperone system. Hsp104/ClpB functionally interact only with their respective Hsp70 system and this specificity is mapped to the Hsp104/ClpB coiled-coil domain (CCD). We hypothesize that the interaction between Hsp70 and Hsp104/ClpB CCD stimulates nucleotide exchange and release of substrate from Hsp70. In the current study, the CCDs of E. coli ClpB and S. cerevisiae Hsp104 have been purified. Isolated domains are monomeric and well folded. They inhibit refolding of aggregated firefly luciferase in a species-specific manner. We found that the ATPase activity of E. coli DnaK is stimulated at low concentrations of the E. coli ClpB CCD but not by yeast Hsp104 CCD. However, in another bacterial system (Thermus thermophilus) we found that the ClpB CCD inhibits The ATPase activity of DnaK suggesting that the interaction may have different consequences in distinct chaperone networks.MAS

The structure of the atypical killer cell immunoglobulin-like receptor, KIR2DL4

The engagement of Natural Killer (NK) cell Immunoglobulin-Like Receptors (KIRs) with their target ligands, Human Leukocyte Antigen (HLA) molecules, is a critical component of innate immunity. Structurally, KIRs typically have either two (D1-D2) or three (D0-D1-D2) extracellular immunoglobulin domains, with the D1 and D2 domain recognizing the α1 and α2 helices of HLA respectively, while the D0 domain of the KIR3DLs binds a loop region flanking the α1 helix of the HLA molecule. KIR2DL4 is distinct from other KIRs (except KIR2DL5) in that it does not contain a D1 domain and instead has a D0-D2 arrangement. Functionally, KIR2DL4 is also atypical in that, unlike all other KIRs, KIR2DL4 has both activating and inhibitory signaling domains. Here, we determined the 2.8 Å crystal structure of the extracellular domains of KIR2DL4. Structurally, KIR2DL4 is reminiscent of other KIR2DL receptors, with the D0 and D2 adopting the C2-type immunoglobulin fold arranged with an acute elbow angle. However, KIR2DL4 self-associated via the D0 domain in a concentration-dependent manner and was observed as a tetramer in the crystal lattice, by size-exclusion chromatography, dynamic light scattering, analytical ultra-centrifugation and small-angle X-ray scattering experiments. The assignment of residues in the D0 domain to forming the KIR2DL4 tetramer precludes an interaction with HLA akin to that observed for KIR3DL1. Accordingly, no interaction was observed to HLA by direct binding studies. Our data suggest that the unique functional properties of KIR2DL4 may be mediated by self-association of the receptor

Microtubule plus-end regulation by centriolar cap proteins

Abstract Centrioles are microtubule-based organelles required for the formation of centrosomes and cilia. Centriolar microtubules, unlike their cytosolic counterparts, grow very slowly and are very stable. The complex of centriolar proteins CP110 and CEP97 forms a cap that stabilizes the distal centriole end and prevents its over-elongation. Here, we used in vitro reconstitution assays to show that whereas CEP97 does not interact with microtubules directly, CP110 specifically binds microtubule plus ends, potently blocks their growth and induces microtubule pausing. Cryo-electron tomography indicated that CP110 binds to the luminal side of microtubule plus ends and reduces protofilament peeling. Furthermore, CP110 directly interacts with another centriole biogenesis factor, CPAP/SAS- 4, which tracks growing microtubule plus ends, slows down their growth and prevents catastrophes. CP110 and CPAP synergize in inhibiting plus-end growth, and this synergy depends on their direct binding. Together, our data reveal a molecular mechanism controlling centriolar microtubule plus- end dynamics and centriole biogenesis

The Structure of the Atypical Killer Cell Immunoglobulin-like Receptor, KIR2DL4

The engagement of Natural Killer (NK) cell Immunoglobulin-Like Receptors (KIRs) with their target ligands, Human Leukocyte Antigen (HLA) molecules, is a critical component of innate immunity. Structurally, KIRs typically have either two (D1-D2) or three (D0-D1-D2) extracellular immunoglobulin domains, with the D1 and D2 domain recognizing the α1 and α2 helices of HLA respectively, while the D0 domain of the KIR3DLs binds a loop region flanking the α1 helix of the HLA molecule. KIR2DL4 is distinct from other KIRs (except KIR2DL5) in that it does not contain a D1 domain and instead has a D0-D2 arrangement. Functionally, KIR2DL4 is also atypical in that, unlike all other KIRs, KIR2DL4 has both activating and inhibitory signaling domains. Here, we determined the 2.8 Å crystal structure of the extracellular domains of KIR2DL4. Structurally, KIR2DL4 is reminiscent of other KIR2DL receptors, with the D0 and D2 adopting the C2-type immunoglobulin fold arranged with an acute elbow angle. However, KIR2DL4 self-associated via the D0 domain in a concentration-dependent manner and was observed as a tetramer in the crystal lattice, by size-exclusion chromatography, dynamic light scattering, analytical ultra-centrifugation and small-angle X-ray scattering experiments. The assignment of residues in the D0 domain to forming the KIR2DL4 tetramer precludes an interaction with HLA akin to that observed for KIR3DL1. Accordingly, no interaction was observed to HLA by direct binding studies. Our data suggest that the unique functional properties of KIR2DL4 may be mediated by self-association of the receptor