RESUMO
Although a strong correlation between jaw mechanics and prey selection has been demonstrated in bony fishes (Osteichthyes), how jaw mechanics influence feeding performance in cartilaginous fishes (Chondrichthyes) remains unknown. Hence, tooth shape has been regarded as a primary predictor of feeding behavior in sharks. Here we apply Finite Element Analysis (FEA) to examine form and function in the jaws of two threatened shark species, the great white (Carcharodon carcharias) and the sandtiger (Carcharias taurus). These species possess characteristic tooth shapes believed to reflect dietary preferences. We show that the jaws of sandtigers and great whites are adapted for rapid closure and generation of maximum bite force, respectively, and that these functional differences are consistent with diet and dentition. Our results suggest that in both taxa, insertion of jaw adductor muscles on a central tendon functions to straighten and sustain muscle fibers to nearly orthogonal insertion angles as the mouth opens. We argue that this jaw muscle arrangement allows high bite forces to be maintained across a wider range of gape angles than observed in mammalian models. Finally, our data suggest that the jaws of sub-adult great whites are mechanically vulnerable when handling large prey. In addition to ontogenetic changes in dentition, further mineralization of the jaws may be required to effectively feed on marine mammals. Our study is the first comparative FEA of the jaws for any fish species. Results highlight the potential of FEA for testing previously intractable questions regarding feeding mechanisms in sharks and other vertebrates.
Assuntos
Força de Mordida , Comportamento Alimentar/fisiologia , Arcada Osseodentária/anatomia & histologia , Arcada Osseodentária/fisiologia , Mastigação/fisiologia , Animais , Fenômenos Biomecânicos , Tubarões/anatomia & histologia , Tubarões/fisiologiaRESUMO
In order to identify new transmembrane helix packing motifs in naturally occurring proteins, we have selected transmembrane domains from a library of random Escherichia coli genomic DNA fragments and screened them for homomultimerization via their abilities to dimerize the bacteriophage lambda cI repressor DNA-binding domain. Sequences were isolated using a modified lambda cI headpiece dimerization assay system, which was shown previously to measure transmembrane helix-helix association in the E. coli inner membrane. Screening resulted in the identification of several novel sequences that appear to mediate helix-helix interactions. One sequence, representing the predicted sixth transmembrane domain (TM6) of the E. coli protein YjiO, was chosen for further analysis. Using site-directed mutagenesis and molecular dynamics, a small set of models for YjiO TM6 multimerization interface interactions were generated. This work demonstrates the utility of combining in vivo genetic tools with computational systems for understanding membrane protein structure and assembly.
Assuntos
Membrana Celular/metabolismo , Proteínas de Ligação a DNA , Proteínas de Escherichia coli/química , Proteínas de Escherichia coli/metabolismo , Escherichia coli , Biblioteca Genômica , Proteínas de Membrana/química , Modelos Moleculares , Motivos de Aminoácidos , Sequência de Aminoácidos , Substituição de Aminoácidos , Bacteriófago lambda/imunologia , Bacteriófago lambda/fisiologia , Sequência de Bases , Sítios de Ligação , Membrana Celular/química , Clonagem Molecular/métodos , Dimerização , Escherichia coli/citologia , Escherichia coli/genética , Escherichia coli/imunologia , Escherichia coli/metabolismo , Proteínas de Escherichia coli/genética , Genes Bacterianos/genética , Vetores Genéticos , Proteínas de Membrana/genética , Proteínas de Membrana/metabolismo , Dados de Sequência Molecular , Ligação Proteica , Sinais Direcionadores de Proteínas/genética , Sinais Direcionadores de Proteínas/fisiologia , Estrutura Quaternária de Proteína , Estrutura Terciária de Proteína , Subunidades Proteicas , Transporte Proteico , Proteínas Recombinantes de Fusão/química , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/metabolismo , Proteínas Repressoras/química , Proteínas Repressoras/metabolismo , Proteínas Virais , Proteínas Virais Reguladoras e AcessóriasRESUMO
A modified (frequency-shifted) Michelson interferometer uses a laser, an acoustooptic cell, and a movable mirror to produce a wide-band FM signal having a center frequency of 80 MHz. The basic concepts are reviewed, and a report of an operating system is given. The angle modulation scheme may be used to produce very wide-band FM or PM. Systems configurations are explored that allow several communication channels in a frequency-division multiplexing arrangement.
