Assembling Nanoparticle Clusters by Kinetic Control Using Weakly Interacting DNA

In this paper, we describe the use of weakly interacting DNA linkages to assemble nanoparticles into defined clusters. Gold nanoparticles (AuNPs) were synthesized and functionalized with thiol modified single-stranded DNA (ssDNA) and hybridized with ssDNA linkers of a defined length (L). The self-assembly kinetics were altered by manipulating interparticle energetics through changes to linker length, rigidity, and sequence. The linker length regulated the hybridization energy between complementary AuNPs, were longer L increased adhesion, resulting in classical uncontrollable aggregation. In contrast, L of six complementary bases decreased adhesion and resulting in slower nucleation that promoted small cluster formation, the growth of which was studied at two assembly temperatures. Results indicated that a decrease in temperature to 15 oC increased cluster yield with L6 as compared to 25 oC. Finally, the clusters were separated from unassembled AuNPs by sucrose gradient ultracentrifugation (UC) and studied via UV-visible spectrophotometry (UV-vis), dynamic light scattering (DLS) and transmission electron microscopy (TEM).

Comparison of methods for purification of bacteriophage lysates of gram-negative bacteria for personalized therapy

Phage therapy is a promising method of treating antibiotic-resistant infections. To obtain a safe therapeutic formulation, bacterial cell components, including endotoxins, must be removed from the phage lysate. This study was aimed at comparing the efficacy of purification methods for phage lysates intended for therapeutic use. Phages vB_KpnM_Seu621 (Myoviridae) and vB_KpnP_Dlv622 (Autographiviridae) were grown using the KP9068 strain of Klebsiella pneumoniae as a host. The obtained lysates were purified using phage precipitation with polyethylene glycol, CsCl density gradient ultracentrifugation, sucrose density gradient ultracentrifugation, precipitation with 100 kDa centrifugal filter units, and phage concentration on 0.22 µm cellulose filters in the presence of MgSO4. Endotoxin concentrations were determined by LAL testing. The obtained lysates contained 1.25 × 1012 ± 7.46 × 1010 and 2.25 × 1012 ± 1.34 × 1011 PFU/ml of vB_KpnM_Seu621 and vB_KpnP_Dlv622, respectively, and had endotoxin concentrations of 3,806,056 ± 429,410 and 189,456 ± 12,406 EU/ml, respectively. CsCl gradient ultracentrifugation was found to be the optimal conventional purification method in terms of reducing endotoxin concentrations and maintaining phage titers (303 ± 20 — 313 ± 35 EU/ml, 1.5–2.75 × 1012 ± 1.71 × 1011 PFU/ml). Sucrose gradient ultracentrifugation and filtration in the presence of MgSO4 were found to be the optimal non-traditional purification methods. A method for phage lysate purification should be selected for each phage preparation individually. Sucrose gradient ultracentrifugation and filtration in the presence of MgSO4 hold promise as purification methods that can produce phage preparations suitable for intravenous administration.

Phosphorylation of CLEC-2 is dependent on lipid rafts, actin polymerization, secondary mediators, and Rac

The C-type lectin-like receptor 2 (CLEC-2) activates platelets through Src and Syk tyrosine kinases via a single cytoplasmic YxxL motif known as a hem immunoreceptor tyrosine-based activation motif (hemITAM). Here, we demonstrate using sucrose gradient ultracentrifugation and methyl-β-cyclodextrin treatment that CLEC-2 translocates to lipid rafts upon ligand engagement and that translocation is essential for hemITAM phosphorylation and signal initiation. HemITAM phosphorylation, but not translocation, is also critically dependent on actin polymerization, Rac1 activation, and release of ADP and thromboxane A2 (TxA2). The role of ADP and TxA2 in mediating phosphorylation is dependent on ligand engagement and rac activation but is independent of platelet aggregation. In contrast, tyrosine phosphorylation of the GPVI-FcRγ-chain ITAM, which has 2 YxxL motifs, is independent of actin polymerization and secondary mediators. These results reveal a unique series of proximal events in CLEC-2 phosphorylation involving actin polymerization, secondary mediators, and Rac activation.

Abstract 488: Sinoatrial Nodal Pacemaker Cells (SANC) Exhibit High Basal CA Activated Adenylyl Cyclase (AC) Activity and Express Multiple Distinctly Localized AC Types

In SANC constituitive AC generates high basal cAMP, inducing PKA-dependent phosphorylation that regulates Ca2+ cycling, that is essential for normal pacemaker function. Our goals were to identify, in rabbit SANC, the types of AC expressed, and their Ca2+ sensitivity and location. Radioimmunoassay (with total phosphodiasterase inhibition) showed a high Ca2+ activated basal AC activity. AC activity increased 5-fold from Ca2+ free (EGTA) to 1 uM free Ca2+. RT PCR (using specifically designed rabbit primers) showed that AC types II and V, and Ca2+ activated types, I and VIII, are expressed in SANC. The organization of these distinct AC types within calveolar or non-calveolar membrane microdomains was determined in pooled SANC isolated from 5 hearts, using triton x100, and sucrose gradient ultracentrifugation. Lipid domains segregated into caveolin containing and non-caveolin containing membrane microdomains, where AC activity was concentrated (fig , AC activity). Immunoblots demonstrated localization of different AC types between these two membrane domains, with AC I, II, V/VI localizing to caveolin containing lipid rafts, and AC VIII present in both caveolin and GM1 lipid domains, and also in the soluble fraction (fig ). In summary, multiple ACs, both Ca2+ activated and non-CA2+ activated types, are expressed in SANC, and these reside in distinct calveolar and non-calveolar lipid domains. We conclude that constituitive basal AC activity is, generated, in part, at least, by a Ca2+ activated AC. type.