Conformational interconversion in protein crystals.

We present evidence that the structure of carbonmonoxy myoglobin crystals can be altered by lowering the pH. This structural change is monitored by the characteristic Fe-CO Raman modes at 508 and 491 cm-1 and is thought to involve a localized distal pocket transition from a "closed" conformation at pH 7 to a more "open" conformation at pH 4. These changes take place in the crystal without loss of intensity of a conformationally sensitive Raman mode at 252 cm-1 that signals a partial unfolding of the globin structure in solution. Quantitative studies, which monitor the open and closed populations as a function of laser photolysis, demonstrate that the interconversion rates (k+/-) in solution at 298 K are fast compared to the photolysis and CO entry rates (i.e. k+/- much greater than 10(3) s-1), while in frozen samples the interconversion is much slower than the experimental time scale (minutes). Since the open conformation is a minority species at pH 7, rapid exchange in aqueous solution is a necessary condition for this species to play a functional role. In the crystal, the interconversion rates are slowed compared to solution and begin to approach the photolysis rate (i.e. k+/- approximately 10(3) to 10(4) s-1). This indicates that the barriers for conformational exchange are increased in the crystal environment, compared to the solution, apparently due to the packing forces of the surrounding molecules. X-ray and neutron diffraction studies of MbCO crystals at high and low pH are needed to characterize the details of the structural changes and to test the hypothesis that closed and open distal pocket structures are associated with the 508 and 491 cm-1 Fe-CO modes.     

A cosmid clone for the 5HT1A receptor (HTR1A) reveals a TaqI RFLP that shows tight linkage to dna loci D5S6, D5S39, and D5S76.

A human neuroreceptor clone (G21), which was isolated by cross-hybridization with the human clone for the beta 2-adrenergic receptor, has recently been shown to encode the gene for the 5HT1A receptor (HTR1A) subtype. In situ hybridization to human metaphase chromosomes mapped the G21 sequence to chromosome 5 at bands 5q11.2-q13. The clone G21 recognizes a SacI RFLP with low heterozygosity (0.13). To increase the informativeness of the HTR1A locus we have isolated two new cosmid clones containing the receptor gene. No polymorphic microsatellites were present in the cosmids. However, one cosmid revealed a new TaqI RFLP that showed tight linkage to new highly polymorphic microsatellites for the loci D5S76, D5S39, and D5S6 in seven British and Icelandic reference pedigrees (maximum LOD of 13.2 with D5S76).     

The circular dichroism of tumor necrosis factor-α: Measurement into the vacuum UV and analysis for secondary structure

The circular dichroism (CD) spectrum of tumor necrosis factor-α has been measured into the vacuum UV to 168 nm. Analysis of the CD for secondary structure is in good agreement with X-ray diffraction results, but the analysis is somewhat unstable. Adding the CD of this protein together with its X-ray determined secondary structure to the basis set should improve subsequent analyses of CD spectra for other all-β proteins.     

Bone marrow transplantation for leukemia and aplastic anemia: management of ABO incompatibility.

Between February 1971 and October 1980, 34 patients with leukemia or aplastic anemia received bone marrow transplants from HLA-identical siblings whose lymphocytes did not react in a mixed leukocyte culture. The donors of 10 patients were ABO-incompatible, and for five pairs the ABO incompatibility was major. Plasma exchanges followed by a red blood cell exchange transfusion reduced the anti-A titres to 1:4 or less in these patients. The ABO incompatibility had no adverse effect on the results of marrow transplantation. Twenty-two patients, including 16 of the 20 who received their transplant after Jan. 1, 1980, are still living. Seven of the 15 patients with acute leukemia have survived 89 to 466 days, and 4 of the 6 with chronic myelogenous leukemia (CML) have survived 117 to 545 days. Of the 13 patients with aplastic anemia, 11 are alive up to 8 years after transplantation. Marrow transplantation, when possible, is the treatment of choice for young patients with acute leukemia in remission and for patients with aplastic anemia. Marrow transplantation may also prove to be effective in patients with CML.     

An improved method for the extraction of corticosterone from cell homogenates and subcellular fractions of the rat adrenal cortex

An improved technique is described for the extraction and analysis of corticosterone (11β,21-dihydroxy-4-pregnene-3,20-dione) from homogenates and subcellular fractions of the rat adrenal cortex. Factors influencing complete extraction of corticosterone were the nature of the organic solvent system and the concentration of the tissue being extracted. The continued activity of steroidogenic enzymes during subcellular fractionation was prevented by 0.1 mM 1-benzylimidazole. For optimum extraction, homogenates were diluted 1:12 (v/v) in 0.25 M sucrose, containing 0.1 M potassium hydroxide. Dilute homogenate was mixed with absolute ethanol (1:10, v/v) and extracted three times with diethyl ether (1:5, v/v). Following extraction, corticosterone in each sample was isolated by thin-layer chromatography (TLC), quantitated by radioimmunoassay (RIA), and corrected by measuring the recovery of added ³H corticosterone. With these procedures, 90–100% of corticosterone found in extracts of adrenal homogenates was recovered in extracts of subcellular fractions of the homogenates.     

Rabies mRNA translation in Xenopus laevis oocytes.

Two rabies virus-specific mRNA species were identified by analysis of their encoded proteins after translation of the partially purified species in Xenopus laevis oocytes. One of these coded for the virion surface glycoprotein (G protein), and the other coded for the major structural protein of the virion nucleocapsid (N protein). The G-mRNA sedimented in a sucrose density gradient at about 18S, and the N-mRNA had a sedimentation coefficient of approximately 16S. Their respective translation products were identified in a radioimmunoassay with specific monoclonal antibody probes that recognized only G or N proteins. Immunoprecipitates formed between the radiolabeled viral antigens synthesized in programmed oocytes and their respective monoclonal antibodies were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The glycoprotein antigen translated from G-mRNA in oocytes migrated in the gel ahead of the virion G protein with a migration rate that was similar to that of nonglycosylated intracellular glycoproteins from virus-infected cells. The results suggested that the branched-chain carbohydrate of G protein was not required for recognition by the particular monoclonal antibody used. The nucleocapsid antigen translated from N-mRNA in oocytes migrated to the same position in the gel as marker virion N protein. Both the electrophoretic mobility of virus-specific antigens in sodium dodecyl sulfate-polyacrylamide gel and the antibody concentration dependence for immunoprecipitations were criteria for identifying the individual viral proteins encoded by the two rabies mRNA's.     

Biochemical markers in a species endangered by introgression: The red wolf

The red wolf (Canis rufus), native to much of the southeastern United States, is endangered by man's activities and by hybridization with other species of the genus Canis. The absence of diagnostic morphological markers to distinguish the red wolf from its hybrids has led to the application of the methods of biochemical genetics to this problem. The finding of a unique electrophoretically determined allele with a distribution congruent with the geographical distribution of the remaining red wolf population is reported.This research was supported by NIH Public Health Service Grants GM 19513 and CA 19311 and by the State of Texas.