The self-assembly in solution of puroindoline-a (Pin-a), an amphiphilic lipid binding protein from common wheat, was investigated by small angle neutron scattering, dynamic light scattering and size exclusion chromatography. Pin-a was found to form monodisperse prolate ellipsoidal micelles with a major axial radius of 112 ± 4.5 Å and minor axial radius of 40.4 ± 0.18 Å. These protein micelles were formed by the spontaneous self-assembly of 38 Pin-a molecules in solution and were stable over a wide pH range (3.5–11) and at elevated temperatures (20–65 °C). Pin-a micelles could be disrupted upon addition of the non-ionic surfactant dodecyl-β-maltoside, suggesting that the protein self-assembly is driven by hydrophobic forces, consisting of intermolecular interactions between Trp residues located within a well-defined Trp-rich domain of Pin-a.
RATIONALE: Cardiac myocyte hypertrophy is the main compensatory response to chronic stress in the heart. p90 ribosomal S6 kinase (RSK) family members are effectors for extracellular signal-regulated kinases that induce myocyte growth. RSK3 contains a unique N-terminal domain that mediates RSK3 binding to the muscle A-kinase anchoring protein (mAKAPβ) scaffold. We have previously published that disruption of RSK3-mAKAPβ complexes using a competing peptide inhibited the phenylephrine-induced hypertrophy of neonatal ventricular myocytes in vitro. In vivo, RSK3 gene deletion in mice attenuated the concentric cardiac hypertrophy induced by pressure overload. We hypothesize that RSK3 anchoring to mAKAPβ in myocytes is required for cardiac hypertrophy in vivo. METHODS AND RESULTS: Adeno-associated viruses (AAV) are gene therapy vectors in development for the treatment of human diseases owing to their nonpathogenic capability for transducing non-dividing cells and their long-term transgene expression. We have used a recombinant AAV2/9 vector to express a mAKAPβ RSK3-binding domain (RBD)-GFP fusion protein under the control of the cardiac myocyte-specific cardiac troponin T promoter. 3 day-old C57BL/6 mice were injected intraperitoneally with either AAV-RBD-GFP or AAV-GFP control virus. At 8 weeks of age mice were subjected to transverse aortic constriction to induce pressure overload (TAC) for two weeks. Cardiac hypertrophy was attenuated in mice injected with the AAV-RBD-GFP virus (biventricular weight indexed to tibial length (mg/mm): 7.7, 8.6, and 9.2 for AAV-RBD, AAV-GFP and non-injected TAC cohorts, respectively; p<0.05 vs. both controls). Echocardiography both corroborated the inhibition of hypertrophy and revealed no deleterious effect on cardiac function attributable to the AAV-RBD-GFP vector. CONCLUSIONS: Anchored RSK3 regulates pathologic myocyte growth. AAV can successfully deliver a competing peptide inhibiting pathological hypertrophy and should be investigated further as a prevention and/or treatment for heart failure.
The interaction between tryptophan-rich puroindoline proteins and model bacterial membranes at the air-liquid interface has been investigated by FTIR spectroscopy, surface pressure measurements, and Brewster angle microscopy. The role of different lipid constituents on the interactions between lipid membrane and protein was studied using wild type (Pin-b) and mutant (Trp44 to Arg44 mutant, Pin-bs) puroindoline proteins. The results show differences in the lipid selectivity of the two proteins in terms of preferential binding to specific lipid head groups in mixed lipid systems. Pin-b wild type was able to penetrate mixed layers of phosphatidylethanolamine (PE) and phosphatidylglycerol (PG) head groups more deeply compared to the mutant Pin-bs. Increasing saturation of the lipid tails increased penetration and adsorption of Pin-b wild type, but again the response of the mutant form differed. The results provide insight as to the role of membrane architecture, lipid composition, and fluidity on antimicrobial activity of proteins. Data show distinct differences in the lipid binding behavior of Pin-b as a result of a single residue mutation, highlighting the importance of hydrophobic and charged amino acids in antimicrobial protein and peptide activity.
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