Biomedical subjects

Keiko Hirose

Publications and source records attributed to Keiko Hirose.

5 recordsLinked to original sources

PubMed2002

Design and functional analysis of actomyosin motor domain chimera proteins.

To gain more structural and functional information on the actomyosin complexes, we have engineered chimera proteins carrying the entire Dictyostelium actin in the loop 2 sequence of the motor domain of Dictyostelium myosin II. Although the chimera proteins were unable to polymerize by themselves, addition of skeletal actin promoted polymerization. Electron microscopic observation demonstrated that the chimera proteins were incorporated into actin filaments, when copolymerized with skeletal actin. Copolymerization with skeletal actin greatly enhanced the MgATPase, while the chimera proteins without added skeletal actin hydrolyzed ATP at a very low rate. These results indicate that the actin part and the motor domain part of the chimera proteins are correctly folded, but the chimera proteins are structurally stressed so that efficient polymerization is inhibited.

Actin Cytoskeleton↗

PubMed2002

Coordination of kinesin's two heads studied with mutant heterodimers.

A conventional kinesin molecule has two identical catalytic domains (heads) and is thought to use them alternately to move processively, with 8-nm steps. To clarify how each head contributes to the observed steps, we have constructed heterodimeric kinesins that consist of two distinct heads. The heterodimers in which one of the heads is mutated in a microtubule-binding loop moved processively, even when the parent mutant homodimers bound too weakly to retain microtubules in microtubule-gliding assays. The velocities of the heterodimers were only slightly higher than those of the mutant homodimers, although mixtures of these weak-binding mutant homodimers and the WT dimers moved microtubules at a velocity similar to the WT. Thus, the mutant head affects the motility of the WT head only when they are in the same molecule. The maximum force a single heterodimer produced in optical trapping nanometry was intermediate between the WT and mutant homodimers, indicating that both heads contribute to the maximum force at the same time. These results demonstrate close collaboration of kinesin's two heads in producing force and motility.

Adenosine Triphosphatases↗

PubMed2002

Dynamics of noise-induced cellular injury and repair in the mouse cochlea.

To assess the dynamics of noise-induced tissue injury and repair, groups of CBA/CaJ mice were exposed to an octave-band noise for 2 hours at levels of 94, 100, 106, 112, or 116 dB SPL and evaluated at survival times of 0, 12, 24 hours or 1, 2, or 8 weeks. Functional change, assessed via auditory brainstem response (ABR), ranged from a reversible threshold shift (at 94 dB) to a profound permanent loss (at 116 dB). Light microscopic histopathology was assessed in serial thick plastic sections and involved quantitative evaluation of most major cell types within the cochlear duct, including hair cells (and their stereocilia), supporting cells, ganglion cells, spiral ligament fibrocytes, spiral limbus fibrocytes, and the stria vascularis. Morphometry allowed patterns of damage to be systematically assessed as functions of (1) cochlear location, (2) exposure level, and (3) postexposure survival. Insights into mechanisms of acute and chronic noise-induced cellular damage are discussed.

Acute Disease↗

PubMed2002

The dynamin A ring complex: molecular organization and nucleotide-dependent conformational changes.

Here we show that Dictyostelium discoideum dynamin A is a fast GTPase, binds to negatively charged lipids, and self-assembles into rings and helices in a nucleotide-dependent manner, similar to human dynamin-1. Chemical modification of two cysteine residues, positioned in the middle domain and GTPase effector domain (GED), leads to altered assembly properties and the stabilization of a highly regular ring complex. Single particle analysis of this dynamin A* ring complex led to a three-dimensional map, which shows that the nucleotide-free complex consists of two layers with 11-fold symmetry. Our results reveal the molecular organization of the complex and indicate the importance of the middle domain and GED for the assembly of dynamin family proteins. Nucleotide-dependent changes observed with the unmodified and modified protein support a mechanochemical action of dynamin, in which tightening and stretching of a helix contribute to membrane fission.

Animals↗

PubMed2002

Pediatric cochlear implants.

Cochlear implants are a safe and effective treatment for children with severe to profound sensorineural hearing loss. As implant technology continues to improve and outcomes are analyzed, younger and younger children are being deemed candidates for implantation. The decision to operate is made after a thorough evaluation by a multidisciplinary team. This review will highlight the preoperative and postoperative issues related to pediatric cochlear implantation.

Age Factors↗