No abstract

Disulfide bonds play an important role in protein folding and stability. However, the cross-linking of sites within proteins by cysteine disulfides has significant distance and dihedral angle constraints. Here we report the genetic encoding of noncanonical amino acids containing long side-chain thiols that are readily incorporated into both bacterial and mammalian proteins in good yields and with excellent fidelity. These amino acids can pair with cysteines to afford extended disulfide bonds and allow cross-linking of more distant sites and distinct domains of proteins. To demonstrate this notion, we preformed growth-based selection experiments at nonpermissive temperatures using a library of random β-lactamase mutants containing these noncanonical amino acids. A mutant enzyme that is cross-linked by one such extended disulfide bond and is stabilized by ∼9°C was identified. This result indicates that an expanded set of building blocks beyond the canonical 20 amino acids can lead to proteins with improved properties by unique mechanisms, distinct from those possible through conventional mutagenesis schemes.noncanonical amino acids | extended disulfide bonds | β-lactamase | thermostability | evolutionary advantage

No abstract

Can semiconductor voltage nanosensors record neuronal signals?

We optimized the performance of quantum confined Stark effect (QCSE)-based voltage nanosensors. A high-throughput approach for single-particle QCSE characterization was developed and utilized to screen a library of such nanosensors. Type-II ZnSe/CdS seeded nanorods were found to have the best performance among the different nanosensors evaluated in this work.The degree of correlation between intensity changes and spectral changes of the exciton's emission under applied field was characterized. An upper limit for the temporal response of individual ZnSe/CdS nanorods to voltage modulation was characterized by high-throughput, high-temporal resolution intensity measurements using a novel photon-counting camera. The measured 3.5 μs response time is limited by the voltage modulation electronics and represents ~ x 30 times higher bandwidth than needed for recording an action potential in a neuron.