The intracellular calcium sensor protein calmodulin (CaM) interacts with a large number of proteins to regulate their biological functions in response to calcium stimulus. This molecular recognition process is diverse in its mechanism, but can be grouped into several classes based on structural and sequence information. We have developed a web-based database (http://calcium.uhnres.utoronto.ca/ctdb) for this family of proteins containing CaM binding sites or, as we propose to call it herein, CaM recruitment signaling (CRS) motifs. At present the CRS motif found in approximately 180 protein sequences in the databases can be divided into four subclasses, each subclass representing a distinct structural mode of molecular recognition involving CaM. The database can predict a putative CRS location within a given protein sequence, identify the subclass to which it may belong, and structural and biophysical parameters such as hydrophobicity, hydrophobic moment, and propensity for alpha-helix formation.

The two interaction surfaces of the dumbbell-shaped calcium-regulatory protein calmodulin (CaM) are rich in the amino acid Met. In this work we have used fluorescence spectroscopy to study the role of these Met residues in binding the single Trp residue that is found in many CaM-binding domain peptides. This approach is facilitated by the absence of Trp residues in CaM. In addition to the wild-type protein, we studied CaM containing the unnatural amino acid selenomethionine (SeMet), which was biosynthetically substituted for its nine Met residues. Furthermore, a CaM mutant protein in which all four Met residues in the C-terminal domain were mutated to Leu, and the N-terminal domain contained either Met or the unnatural SeMet, was studied. The Trp fluorescence quantum yield of many Trp-containing CaM-binding peptides increases upon binding to calcium-CaM. Moreover, the emission wavelength of the Trp fluorescence is blue-shifted from 353 to 325-333 nm. These parameters indicate movement of Trp from a solvent exposed to a hydrophobic environment. The fluorescence results obtained with these four CaM variants showed that Se is very effective at quenching Trp fluorescence in the calmodulin-bound peptides from myosin light chain kinase (MLCK) and CaM kinase I, while S is somewhat effective (Se > S > C). The quenching effect is markedly distance dependent, as it only influences the Trp residue of the bound peptide (<=7 A) but has little effect on the two Tyr residues in the C-terminal domain of CaM (>=10 A). Since the Trp fluorescence quenching is very dramatic, the protein containing Leu's in the C-terminal domain and SeMet's in the N-terminal domain allowed us to directly determine the orientation of the MLCK and CaM kinase I peptides bound to CaM; in both cases the Trp residue binds to the C-terminal domain of CaM. Our data indicate that SeMet quenching of Trp fluorescence could become a simple and useful tool for studies of protein folding, and protein-protein and protein-peptide interactions.

Fabrication of soft piezoelectric nanomaterials is essential for the development of wearable and implantable biomedical devices. However, a big challenge in this soft functional material development is to achieve a high piezoelectric property with long‐term stability in a biological environment. Here, a one‐step strategy for fabricating core/shell poly(vinylidene difluoride) (PVDF)/dopamine (DA) nanofibers (NFs) with a very high β‐phase content and self‐aligned polarization is reported. The self‐assembled core/shell structure is believed essential for the formation and alignment of β‐phase PVDF, where strong intermolecular interaction between the NH2 groups on DA and the CF2 groups on PVDF is responsible for aligning the PVDF chains and promoting β‐phase nucleation. The as‐received PVDF/DA NFs exhibit significantly enhanced piezoelectric performance and excellent stability and biocompatibility. An all‐fiber‐based soft sensor is fabricated and tested on human skin and in vivo in mice. The devices show a high sensitivity and accuracy for detecting weak physiological mechanical stimulation from diaphragm motions and blood pulsation. This sensing capability offers great diagnostic potential for the early assessment and prevention of cardiovascular diseases and respiratory disorders.