Removal of a C-terminal serine residue proximal to the inter-chain disulfide bond of a human IgG1 lambda light chain mediates enhanced antibody stability and antibody dependent cell-mediated cytotoxicity

Optimization of biophysical properties is a critical success factor for the developability of monoclonal antibodies with potential therapeutic applications. The inter-domain disulfide bond between light chain (Lc) and heavy chain (Hc) in human IgG1 lends structural support for antibody scaffold stability, optimal antigen binding, and normal Fc function. Recently, human IgG1λ has been suggested to exhibit significantly greater susceptibility to reduction of the inter Lc-Hc disulfide bond relative to the same disulfide bond in human IgG1κ. To understand the molecular basis for this observed difference in stability, the sequence and structure of human IgG1λ and human IgG1κ were compared. Based on this Lc comparison, three single mutations were made in the λ Lc proximal to the cysteine residue, which forms a disulfide bond with the Hc. We determined that deletion of S214 (dS) improved resistance of the association between Lc and Hc to thermal stress. In addition, deletion of this terminal serine from the Lc of IgG1λ provided further benefit, including an increase in stability at elevated pH, increased yield from transient transfection, and improved in vitro antibody dependent cell-mediated cytotoxicity (ADCC). These observations support the conclusion that the presence of the terminal serine of the λ Lc creates a weaker inter-chain disulfide bond between the Lc and Hc, leading to slightly reduced stability and a potential compromise in IgG1λ function. Our data from a human IgG1λ provide a basis for further investigation of the effects of deleting terminal serine from λLc on the stability and function of other human IgG1λ antibodies.     

AUXIN RESPONSE FACTOR 2 Intersects Hormonal Signals in the Regulation of Tomato Fruit Ripening

The involvement of ethylene in fruit ripening is well documented, though knowledge regarding the crosstalk between ethylene and other hormones in ripening is lacking. We discovered that AUXIN RESPONSE FACTOR 2A (ARF2A), a recognized auxin signaling component, functions in the control of ripening. ARF2A expression is ripening regulated and reduced in the rin, nor and nr ripening mutants. It is also responsive to exogenous application of ethylene, auxin and abscisic acid (ABA). Over-expressing ARF2A in tomato resulted in blotchy ripening in which certain fruit regions turn red and possess accelerated ripening. ARF2A over-expressing fruit displayed early ethylene emission and ethylene signaling inhibition delayed their ripening phenotype, suggesting ethylene dependency. Both green and red fruit regions showed the induction of ethylene signaling components and master regulators of ripening. Comprehensive hormone profiling revealed that altered ARF2A expression in fruit significantly modified abscisates, cytokinins and salicylic acid while gibberellic acid and auxin metabolites were unaffected. Silencing of ARF2A further validated these observations as reducing ARF2A expression let to retarded fruit ripening, parthenocarpy and a disturbed hormonal profile. Finally, we show that ARF2A both homodimerizes and interacts with the ABA STRESS RIPENING (ASR1) protein, suggesting that ASR1 might be linking ABA and ethylene-dependent ripening. These results revealed that ARF2A interconnects signals of ethylene and additional hormones to co-ordinate the capacity of fruit tissue to initiate the complex ripening process.     

Protein fishing with chiral molecular baits

Chirality plays a central role in various biological recognition processes. Here a methodology was developed to utilize chiral recognition processes for the selective biotinylation of proteins in crude cell lysates. Two pairs of diastereomeric probes containing benzophenone and biotin were prepared through solid-phase synthesis. Protein-binding selectivity of each probe was examined by photo-cross-linking of cell lysates, followed by SDS-PAGE and Western blot. The study revealed that our approach permits selective labeling of benzophenone-binding proteins in complex proteomes. In addition, it was found that the selectivity depends largely on a single chiral center and substitutions in the vicinity of benzophenone. Taken together, the current work demonstrates that chiral recognition process can be employed to selectively label proteins in complex proteomes. Thus the study opens up the possibility to expand the scope of chemical proteomics research for various applications, including biomarker discovery, drug screening and development.     

Development of a metabolic network design and optimization framework incorporating implementation constraints: a succinate production case study

We have developed a pathway design and optimization scheme that accommodates genetically and/or environmentally derived operational constraints. We express the full set of theoretically optimal pathways in terms of the underlying elementary flux modes and then examine the sensitivity of the optimal yield to a wide class of physiological perturbations. Though the scheme is general it is best appreciated in a concrete context: we here take succinate production as our model system. The scheme produces novel pathway designs and leads to the construction of optimal succinate production pathway networks. The model predictions compare very favorably with experimental observations.     

PKCθ is required for hemostasis and positive regulation of thrombin-induced platelet aggregation and α-granule secretion

Platelet activation due to vascular injury is essential for hemostatic plug formation, and is mediated by agonists, such as thrombin, which trigger distinct receptor-coupled signaling pathways. Thrombin is a coagulation protease, which activates G protein-coupled protease-activated receptors (PARs) on the surface of platelets. We found that C57BL/6J and BALB/C mice that are deficient in protein kinase C θ (PKCθ), exhibit an impaired hemostasis, and prolonged bleeding following vascular injury. In addition, murine platelets deficient in PKCθ displayed an impaired thrombin-induced platelet activation and aggregation response. Lack of PKCθ also resulted in impaired α-granule secretion, as demonstrated by the low surface expression of CD62P, in thrombin-stimulated platelets. Since PAR4 is the only mouse PAR receptor that delivers thrombin-induced activation signals in platelets, our results suggest that PKCθ is a critical effector molecule in the PAR4-linked signaling pathways and in the regulation of normal hemostasis in mice.     

Selective photolabeling of Lck kinase in complex proteome

A molecular probe that selectively tags Lck, a Src-family kinase, was developed. This probe was one of many compounds originally designed to target the active site of tyrosine kinases in general. To our surprise, however, the probe almost exclusively labeled Lck even in a lysate of Jurkat cells. This finding led us to further characterize this probe-Lck complex by a series of photolabeling and mass spectrometric analyses. The probe-binding site on Lck was located within the well-conserved region of Src-family kinases, as we originally expected. However, the unexpected selectivity of this probe toward Lck suggests that subtle factors, which are difficult to predict based on static crystal structures, play important roles in probe recognition.     

Protein kinase C-theta in platelet activation

Members of the protein kinase C (PKC) family of serine/threonine kinases have been implicated in several physiological processes regulating the activation response of platelets. They are involved in processes leading to granule secretion, integrin activation, platelet aggregation and spreading, and procoagulation. The protein kinase C θ (PKCθ) isoform, which was originally identified in T lymphocytes, is also expressed at relatively high levels in platelets, wherein it is involved in the regulation of hemostasis and thrombosis. Recent studies suggest a role for PKCθ in protease-activated receptor (PAR)-, glycoprotein VI (GPVI) receptor- and glycoprotein α(IIb)β(3) integrin receptor-linked signal transduction pathways. The present review focuses on the latest observations relevant to the role of PKCθ in platelet activation.