Neuropharmacology. Odorants may arouse instinctive behaviours.
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Animals↗
Biomedical subjects
B Malnic
Publications and source records attributed to B Malnic.
Combinatorial receptor codes for odors.
The discriminatory capacity of the mammalian olfactory system is such that thousands of volatile chemicals are perceived as having distinct odors. Here we used a combination of calcium imaging and single-cell RT-PCR to identify odorant receptors (ORs) for odorants with related structures but varied odors. We found that one OR recognizes multiple odorants and that one odorant is recognized by multiple ORs, but that different odorants are recognized by different combinations of ORs. Thus, the olfactory system uses a combinatorial receptor coding scheme to encode odor identities. Our studies also indicate that slight alterations in an odorant, or a change in its concentration, can change its "code," potentially explaining how such changes can alter perceived odor quality.
Amino Acid Sequence↗
Regulatory properties of the NH2- and COOH-terminal domains of troponin T. ATPase activation and binding to troponin I and troponin C.
The contraction of skeletal muscle is regulated by Ca2+ binding to troponin C, which results in an internal reorganization of the interactions within the troponin-tropomyosin complex. Troponin T is necessary for Ca2+-dependent inhibition and activation of actomyosin. Troponin T consists of an extended NH2-terminal domain that interacts with tropomyosin and a globular COOH-terminal domain that interacts with tropomyosin, troponin I, and troponin C. In this study we used recombinant troponin T and troponin I fragments to delimit further the structural and regulatory interactions with the thin filament. Our results show the following: (i) the NH2-terminal region of troponin T activates the actomyosin ATPase in the presence of tropomyosin; (ii) the interaction of the globular domain of troponin T with the thin filament blocks ATPase activation in the absence of Ca2+; and (iii) the COOH-terminal region of the globular domain anchors the troponin C-troponin I binary complex to troponin T through a direct Ca2+-independent interaction with the NH2-terminal region of troponin I. This interaction is required for Ca2+-dependent activation of the actomyosin ATPase activity. Based on these results we propose a refined model for the troponin complex and its interaction with the thin filament.
Animals↗
Structural interactions responsible for the assembly of the troponin complex on the muscle thin filament.
Skeletal muscle contraction is regulated by a complex of five polypeptides which are stably associated with the actin filament. This complex consists of two proteins: troponin with three subunits (TnC; TnI and TnT) and tropomyosin (a dimer of two chains). Using deletion mutants of TnC, TnI and TnT we determined that each of these polypeptides can be divided into at least two domains. One domain is responsible for the regulatory properties of the protein. Its interaction with the other components of the system change upon calcium binding to TnC. A second domain present in each of these proteins is responsible for the stable association of the complex to the actin filament. The interactions among this second set of domains is not influenced by calcium binding to TnC. The structural interactions are: 1) interactions between the C-domain of TnC with the N-domain of TnI; 2) interactions of the N-domain of TnI with the C-terminal domain of TnT and 3) interactions between the N-domain of TnT (T1) and actin/tropomyosin.
Actin Cytoskeleton↗
Assembly of functional skeletal muscle troponin complex in Escherichia coli.
The production of multi-subunit proteins of eukaryotic origin in Escherichia coli usually relies on the different subunits being expressed individually and the protein being reassembled in vitro. Here we describe the construction and characterization of plasmids capable of coexpressing the three subunits of chicken skeletal muscle troponin complex in E. coli. We demonstrate that the troponin subunits assembled in the cytoplasm of E. coli cell are fully functional. The troponin complex was purified to homogeneity in high yields. When reconstituted into actin filaments, the complex assembled in vivo was capable of regulating the myosin ATPase with a calcium dependence that was identical to the complex reconstituted in vitro. These results demonstrate that the coexpression of the subunits of a protein complex can prevent the accumulation of denatured proteins in inclusion granules.
Animals↗