Biomedical subjects

H H Jerng

Publications and source records attributed to H H Jerng.

5 recordsLinked to original sources

PubMed1999

Inactivation gating of Kv4 potassium channels: molecular interactions involving the inner vestibule of the pore.

Kv4 channels represent the main class of brain A-type K+ channels that operate in the subthreshold range of membrane potentials (Serodio, P., E. Vega-Saenz de Miera, and B. Rudy. 1996. J. Neurophysiol. 75:2174- 2179), and their function depends critically on inactivation gating. A previous study suggested that the cytoplasmic NH2- and COOH-terminal domains of Kv4.1 channels act in concert to determine the fast phase of the complex time course of macroscopic inactivation (Jerng, H.H., and M. Covarrubias. 1997. Biophys. J. 72:163-174). To investigate the structural basis of slow inactivation gating of these channels, we examined internal residues that may affect the mutually exclusive relationship between inactivation and closed-state blockade by 4-aminopyridine (4-AP) (Campbell, D.L., Y. Qu, R.L. Rasmussen, and H.C. Strauss. 1993. J. Gen. Physiol. 101:603-626; Shieh, C.-C., and G.E. Kirsch. 1994. Biophys. J. 67:2316-2325). A double mutation V[404,406]I in the distal section of the S6 region of the protein drastically slowed channel inactivation and deactivation, and significantly reduced the blockade by 4-AP. In addition, recovery from inactivation was slightly faster, but the pore properties were not significantly affected. Consistent with a more stable open state and disrupted closed state inactivation, V[404,406]I also caused hyperpolarizing and depolarizing shifts of the peak conductance-voltage curve ( approximately 5 mV) and the prepulse inactivation curve (>10 mV), respectively. By contrast, the analogous mutations (V[556,558]I) in a K+ channel that undergoes N- and C-type inactivation (Kv1.4) did not affect macroscopic inactivation but dramatically slowed deactivation and recovery from inactivation, and eliminated open-channel blockade by 4-AP. Mutation of a Kv4-specific residue in the S4-S5 loop (C322S) of Kv4.1 also altered gating and 4-AP sensitivity in a manner that closely resembles the effects of V[404, 406]I. However, this mutant did not exhibit disrupted closed state inactivation. A kinetic model that assumes coupling between channel closing and inactivation at depolarized membrane potentials accounts for the results. We propose that components of the pore's internal vestibule control both closing and inactivation in Kv4 K+ channels.

4-Aminopyridine↗

PubMed1997

K+ channel inactivation mediated by the concerted action of the cytoplasmic N- and C-terminal domains.

We have examined the molecular mechanism of rapid inactivation gating in a mouse Shal K+ channel (mKv4.1). The results showed that inactivation of these channels follows a complex time course that is well approximated by the sum of three exponential terms. Truncation of an amphipathic region at the N-terminus (residues 2-71) abolished the rapid phase of inactivation (r = 16 ms) and altered voltage-dependent gating. Surprisingly, these effects could be mimicked by deletions affecting the hydrophilic C-terminus. The sum of two exponential terms was sufficient to describe the inactivation of deletion mutants. In fact, the time constants corresponded closely to those of the intermediate and slow phases of inactivation observed with wild-type channels. Further analysis revealed that several basic amino acids at the N-terminus do not influence inactivation, but a positively charged domain at the C-terminus (amino acids 420-550) is necessary to support rapid inactivation. Thus, the amphipathic N-terminus and the hydrophilic C-terminus of mKv4.1 are essential determinants of inactivation gating and may interact with each other to maintain the N-terminal inactivation gate near the inner mouth of the channel. Furthermore, this inactivation gate may not behave like a simple open-channel blocker because channel blockade by internal tetraethylammonium was not associated with slower current decay and an elevated external K+ concentration retarded recovery from inactivation.

Animals↗

PubMed1993

Surfactant protein A-binding proteins. Characterization and structures.

An alveolar cell membrane protein acts as a surfactant protein A (SP-A) receptor; it binds SP-A and regulates surfactant secretion. We identified such alveolar cell membrane SP-A-binding proteins using anti-idiotype antibodies directed against the surfactant protein binding region of anti-surfactant antibodies. These monoclonal anti-idiotype antibodies, A2C and A2R, also recognize an alveolar cell membrane protein of approximately 30 kDa. A pulmonary protein of approximately 30 kDa binds SP-A. Unique cDNAs encoding this protein were identified in human (4.1-kilobase) and porcine (1.8-kilobase) lung expression libraries. Coding regions of these cDNAs cross-hybridize with each other under stringent conditions. Both cDNAs encode similar approximately 32-kDa proteins that bind SP-A. The human and porcine SP-A recognition (SPAR) proteins resemble each other, as well as other cell membrane receptors. Their projected structures are consistent with cell membrane receptors. Recombinant human and porcine SPAR proteins bind SP-A as well as the two anti-idiotype antibodies just as do native lung proteins of approximately 30 kDa. SPAR transcripts are expressed primarily in lung. The cellular distribution of these transcripts, as determined by in situ hybridization, is similar to that of SPAR protein, as determined by immunohistochemistry; both are found in cells consistent with type II pneumocytes. SPAR-producing cells resemble the alveolar cells expressing SP-B and SP-C transcripts in appearance, location, and distribution. Therefore, cDNAs for pulmonary SP-A-binding proteins from two disparate species have been isolated and sequenced, and the recombinant proteins they encode bind the same ligand. Further structural, functional, and genetic studies of these proteins may help explain how pulmonary surfactant secretion is regulated.

Amino Acid Sequence↗

PubMed1992

Sequence and analysis of the BamHI "D" fragment of Shope fibroma virus: comparison with similar regions of related poxviruses.

Differences observed in the virulence of two related leporipoxviruses are closely tied to a particular region of their genomes. For the virulent poxvirus of this pair, malignant rabbit fibroma virus (MV), this region is the BamHI "C" fragment, which is 10.7 kb. For the avirulent poxvirus, Shope fibroma virus, SFV, this region is the corresponding BamHI "D" fragment, which is 13.1 kb. As part of our attempt to understand the virulence of these two viruses, we sequenced these two DNA fragments. The sequence for the BamHI "C" fragment of MV is reported elsewhere (Strayer et al., 1991). We report here the sequence for SFV's BamHI "D" fragment and resultant open reading frames, and compare both DNA and open reading frame structures to those of MV and other known poxviruses. The BamHI "D" fragment of SFV contains 12 open reading frames of 100 amino acids or more, arranged similarly to orf's in MV and vaccinia. Striking similarities between SFV and MV are seen in certain parts of this restriction fragment, including substantial stretches of DNA in which the two viruses are identical. Clear homologies exist between these leporipox virus genomes and those of other related poxviruses. To understand the pathogenesis of virus infection, one must appreciate the structure of those viral genes that play important roles in infection.

Base Sequence↗

PubMed1991

Sequence and analysis of a portion of the genomes of Shope fibroma virus and malignant rabbit fibroma virus that is important for viral replication in lymphocytes.

The 10.7-kb BamHI "C" restriction fragment of malignant rabbit fibroma virus (MV) contains genes that are important for its immunosuppressive activity. When this fragment is transferred to a related avirulent leporipoxvirus, Shope fibroma virus (SFV), recombinant viruses show clinical features characteristic of MV: they replicate in lymphocytes and alter immune function in vitro, induce disseminated tumors in recipient rabbits, and are immunosuppressive in vivo. The 10.7-kb BamHI "C" restriction fragment of MV was sequenced in its entirety. Its DNA sequence and the 14 ORF's derived from analyzing this sequence are discussed. Analysis of known open reading frames to which the ORF's from MV's Bam "C" fragment show homology permits us to identify some MV ORF's showing high degrees of similarity to known and postulated proteins produced by vaccinia virus. Functions for some of these vaccinia proteins are known, while functions for others are hypothetical or unknown. Further analysis of genetic determinants of MV's virulence has indicated that two overlapping restriction subfragments of the BamHI "C" fragment can transfer MV's virulent behavior to SFV. The 0.7-kb region in which these two subfragments overlap includes the C-terminus of MV orf C-7 and the N terminus of MV orf C-8. These correspond to the C- and N-termini, respectively, of SFV orf's D-9 and D-10 and to vaccinia orf's D-6 (early transcription factor) and D-7 (subunit of RNA polymerase). We sequenced the region of SFV's BamHI "D" fragment in this area and illustrate here the comparative sequences of this portion of SFV's genome and orf's. On the basis of comparisons between MV, SFV, and vaccinia in this area we discuss the potential significance of these observations.

Amino Acid Sequence↗