A novel NH(2)-terminal, nonhydrophobic motif targets a male germ cell-specific hexokinase to the endoplasmic reticulum and plasma membrane

Although three germ cell-specific transcripts of type 1 hexokinase exist in murine male germ cells, only one form, HK1-sc, is found at the protein level. This single isoform localizes to three distinct structures in mouse spermatozoa: the membranes of the head, the mitochondria in the midpiece, and the fibrous sheath in the flagellum (Travis, A. J., Foster, J. A., Rosenbaum, N. A., Visconti, P. E., Gerton, G. L., Kopf, G. S., and Moss, S. B. (1998) Mol. Biol. Cell 9, 263-276). The mechanism by which one protein is targeted to multiple sites within this highly polarized cell poses important questions of protein targeting. Because the study of protein targeting in germ cells is hampered by the lack of established cell lines in culture, constructs containing different domains of the germ cell-specific hexokinase transcripts were linked to a green fluorescent protein and transfected into hexokinase-deficient M+R42 cells. Constructs containing a nonhydrophobic, germ cell-specific domain, present at the amino terminus of the HK1-SC protein, were targeted to the endoplasmic reticulum and the plasma membrane. Mutational analysis of this domain demonstrated that a complex motif, PKIRPPLTE (with essential residues italicized), represented a novel endoplasmic reticulum-targeting motif. Constructs based on another germ cell-specific hexokinase transcript, HK1-sa, demonstrated the specific proteolytic removal of an amino-terminal domain, resulting in a protein product identical to HK1-SC. Such processing might constitute a regulatory mechanism governing the spatial and/or temporal expression of the protein.

Identification of a novel PSD-95/Dlg/ZO-1 (PDZ)-like protein interacting with the C terminus of presenilin-1

Presenilin-1 (PS-1) is the most causative Alzheimer gene product, and its function is not well understood. In an attempt to elucidate the function of PS-1, we screened a human brain cDNA library for PS-1-interacting proteins using the yeast two-hybrid system and isolated a novel protein containing a PSD-95/Dlg/ZO-1 (PDZ)-like domain. This novel PS-1-associated protein (PSAP) shares a significant similarity with a Caenorhabditis elegans protein of unknown function. Northern blot analysis revealed that PSAP is predominantly expressed in the brain. Deletion of the first four C-terminal amino acid residues of PS-1, which contain the PDZ domain-binding motif (Gln-Phe-Tyr-Ile), reduced the binding activity of PS-1 toward PSAP 4-fold. These data suggest that PS-1 may associate with a PDZ-like domain-containing protein in vivo and thus may participate in receptor or channel clustering and intracellular signaling events in the brain.

Identification and characterization of glycoprotein H of MDV-1 GA strain

A 2439 bp open reading frame (ORF) was identified from the DNA sequence of BamHI-F and -K2 fragments of Marek's disease virus of serotype 1 (MDV-1) GA strain, which predicts an 813 amino acid polypeptide. This peptide is homologous to HSV-1 gH, and has typical glycoprotein features. There are nine potential N-linked glycosylation sites within the extracellular domain. A fragment of the gH ORF was cloned into pGEX vector in frame with glutathione S-transferase (GST) to produce a GST-gH fusion protein in Escherichia coli. The GST-gH fusion protein was used to develop gH monoclonal and polyclonal antibodies. Expression of gH was detected in duck embryo fibroblasts (DEFs) infected with MDV-1 GA strain by immunofluorescence assay (IFA) with these antibodies. Virus neutralization and plaque-forming inhibition analyses were conducted with the gH antiserum. There were no neutralization and plaque-forming inhibition activities of gH antiserum. Comparison of the DNA sequence of gH gene between GA and RB1B strains of MDV-1 revealed major difference in the upstream control elements of gH ORF.

Identification and structural analysis of a MDV gene encoding a protein kinase

DNA sequence analysis of the BamHI-C fragment of Marek's Disease Virus (MDV) reveals the presence of a 513 amino acid open reading frame (ORF). This ORF codes for a protein with an estimated M(r) of 58,901. Comparison of the amino acid sequence with those available in the Swiss-Prot database indicates extensive homology with a protein kinase (PK) of herpes simplex virus (HSV) and varicella-zoster virus (VZV). In Northern blot hybridization, a transcript of 2.0 kb was detected in MDV (GA strain) infected duck embryo fibroblasts (DEFs). A portion of the ORF was expressed in Escherichia coli as a trpE-fusion protein and used to generate antiserum in New Zealand rabbits. This antiserum specifically detected a protein of 60 kDa in MDV serotype 1, 2 and 3 infected DEFs or chicken embryo fibroblasts (CEFs) by Western blot analysis. This ORF codes for a functional PK.

Combination of intraoperative embolization with surgical resection for treatment of giant cerebral arteriovenous malformation

OBJECTIVE

To reduce the risk of surgical resection of giant arteriovenous malformation (AVM) (> 6.0 cm) and prevent normal perfusion pressure breakthrough (NPPB) for lowering the postoperative mortality.

METHODS

During the operation under barbiturate anesthesia, the proximal end of the feeding arteries were ligated at first, and 0.5 ml isobutyl 12-cyanoacrylate (IBCA) with 0.5 ml 5% glucose was injected into the vessels towards the AVM, then the malformed vessels were resected totally. Postoperative digital subtraction angiography of the four vessels was performed in all patients.

RESULTS

50 patients with giant AVM survived after operation, only 6 (12.0%) had transient neurological dysfunction and 44 (88.0%) recovered after a follow-up of 6-36 months. No patient suffered from normal perfusion pressure breakthrough (NPPB).

CONCLUSIONS

The embolization could block the arteriovenous shunts sufficiently to decrease the blood flow away from the normal areas of the brain so as to prevent the incidence of intra- and postoperative rebleeding, especially in NPPB. Therefore, the combination of intraoperative embolization with surgical resection is an effective strategy in the treatment of giant cerebral AVMs, which make it operable for those used to be regarded as inoperable cases.

Structural determinants for the intracellular localization of the isozymes of mammalian hexokinase: intracellular localization of fusion constructs incorporating structural elements from the hexokinase isozymes and the green fluorescent protein

Fusion constructs incorporating structural elements from mammalian isozymes of hexokinase, Types I-IV, in frame with sequence encoding the green fluorescent protein (GFP) have been made and expressed in hexokinase-deficient M + R 42 cells. Fusion proteins incorporating catalytically active regions from the Type II isozyme, or the entire Type IV sequence, were expressed in catalytically active form. The intracellular localization of the fusion proteins was determined using confocal microscopy. Fusion proteins including the N-terminal halves of the Type I or Type II isozymes were targeted to mitochondria, while the N-terminal half of the Type III isozyme did not confer mitochondrial targeting. The mitochondrial targeting signal was represented by the hydrophobic sequence at the extreme N-termini ("binding domain") of the Type I and Type II isozymes. Inclusion of the binding domain from the Type I isozyme was sufficient to confer mitochondrial binding on GFP itself as well as on constructs including the N-terminal half of Type III hexokinase. However, the Type I hexokinase binding domain was not sufficient to cause mitochondrial targeting of a construct containing the Type IV sequence. These results suggest that, although the binding domain is critical for mitochondrial targeting, other interactions involving an adjacent structure might also play a role. Fusion proteins including the N-terminal half of Type I hexokinase became dissociated from mitochondria under conditions favorable for accumulation of intracellular Glc-6-P. The 2-deoxy analog was much less effective than Glc in causing mitochondrial dissociation of the fusion construct, in accord with previous studies showing 2-deoxy-Glc-6-P to be much less effective than Glc-6-P at promoting release of Type I hexokinase from mitochondria. Dissociation, induced by formation of Glc-6-P or 2-deoxy-Glc-6-P, did not occur with the fusion protein including only the binding domain of Type I hexokinase. This is consistent with previous studies indicating that Glc-6-P-dependent dissociation results from binding of this ligand to a site in the N-terminal half of the enzyme, but which is not likely to be present in the small segment represented by the binding domain. These studies demonstrate the usefulness of this approach in defining structural elements involved in targeting hexokinase isozymes to specific subcellular locations and modulation of that intracellular location by perturbations of metabolic status.

Identification and characterization of a Marek's disease virus gene encoding DNA polymerase

DNA sequence analysis revealed a gene encoding the Marek's disease virus (MDV) DNA polymerase (pol) within the BamHI-E fragment of the long unique region of the virus genome. Identification is based on an extensive amino acid homology between the MDV open reading frame and the DNA pol (UL30) of the herpes simplex virus. We describe here a 3540-base-pair fragment of the MDV DNA encoding 1180 amino acids with a M(r) of 133,920 daltons as the viral DNA pol gene, with the analysis of transcription and translation. In Northern blot hybridization, a transcript of 4.0 kb was detected in GA-MDV-infected duck embryo fibroblast (DEF) cells. An antiserum was generated in rabbit using TryE-pol fusion protein expressed in E. coli. This antiserum specifically immunoprecipitated a protein of 135 kD from lysates of MDV-GA-infected DEF cells. MDV DNA pol showed extensive homology to five distantly related herpesviruses: equine herpesvirus (EHV), varicella-zoster virus (VZV), herpes simplex virus type 1 (HSV-1), Epstein-Barr virus (EBV), and human cytomegalovirus (HCMV). Comparison of amino acid sequences among the herpesviruses highlights nine highly conserved regions. Three of the conserved regions are in the N-terminus in the 3'-5' exonuclease domains and the remaining six are in the C-terminus in the catalytic domains. The predicted structural characters are in good agreement with the published data on a number of human herpesvirus DNA pol. The identification of MDV DNA pol gene may lead to a better understanding of MDV replication.