Higher-order interactions of Bcr-Abl can broaden chronic myeloid leukemia (CML) drug repertoire

Bcr-Abl, a nonreceptor tyrosine kinase, is associated with leukemias, especially chronic myeloid leukemia (CML). Deletion of Abl's N-terminal region, to which myristoyl is linked, renders the Bcr-Abl fusion oncoprotein constitutively active. The substitution of Abl's N-terminal region by Bcr enables Bcr-Abl oligomerization. Oligomerization is critical: it promotes clustering on the membrane, which is essential for potent MAPK signaling and cell proliferation. Here we decipher the Bcr-Abl specific, step-by-step oligomerization process, identify a specific packing surface, determine exactly how the process is structured and identify its key elements. Bcr's coiled coil (CC) domain at the N-terminal controls Bcr-Abl oligomerization. Crystallography validated oligomerization via Bcr-Abl dimerization between two Bcr CC domains, with tetramerization via tight packing between two binary assemblies. However, the structural principles guiding Bcr CC domain oligomerization are unknown, hindering mechanistic understanding and drugs exploiting it. Using molecular dynamics (MD) simulations, we determine that the binary complex of the Bcr CC domain serves as a basic unit in the quaternary complex providing a specific surface for dimer–dimer packing and higher-order oligomerization. We discover that the small α1-helix is the key. In the binary assembly, the helix forms interchain aromatic dimeric packing, and in the quaternary assembly, it contributes to the specific dimer–dimer packing. Our mechanism is supported by the experimental literature. It offers the key elements controlling this process which can expand the drug discovery strategy, including by Bcr CC-derived peptides, and candidate residues for small covalent drugs, toward quenching oligomerization, supplementing competitive and allosteric tyrosine kinase inhibitors.     

Habitat use and support preference of two free-ranging saltatory lemurs (Lepilemur edwardsi and Avahi occidentalis)

Lepilemur edwardsi and Avahi occidentalis are two species of nocturnal, folivorous 'vertical clingers and leapers' (VCL). They have a similar body mass and share the same morphological adaptation for leaping. In a field study under sympatric conditions at Ampijoroa, Madagascar, comparison of support use with support availability using Jacobs' D preference values (Jacobs, 1974) showed that both species actively chose or avoided branches with certain qualities. However, while both species showed a preference for small oblique and horizontal branches, they selected them at different heights in the forest and with varying degrees of preference and avoidance for the other available supports. Despite their traditional locomotor assignation, both species showed a surprisingly strong preference for horizontal supports. These striking variations in detail of support preference may aid the maintenance of species segregation and niche difference.     

500 MHz H-NMR studies of bile salt-phosphatidylcholine mixed micelles and vesicles Evidence for differential motional restraint on bile salt and phosphatidylcholine resonances

¹H nuclear magnetic resonance (NMR) spectra at 500 MHz have been obtained for taurocholate/egg phosphatidylcholine mixtures of varying composition. The excellent chemical shift dispersion permits identification of most resonances for each component. This high-resolution character of the NMR spectra is retained until the phosphatidylcholine (PC) mole fraction exceeds 60–70% (the exact limit depends on ionic strength). ¹H linewidths have been monitored as a function of solute composition in order to evaluate trends in local molecular mobility of each component as the distribution of aggregate particles is varied, and to examine the effects of added NaCl in altering micellar size and shape. Although prior light scattering studies (Mazer, N.A., Benedek, G.B. and Carey, M.C. (1980) Biochemistry 19, 601–615) and our own work indicate a 6-fold increase in particle hydrodynamic radius from pure taurocholate micelles to 1 : 1 taurocholate/PC mixtures containing 150 mM NaCl, both lipid components retain substantial motional freedom and exhibit narrow NMR signals in this compositional region. As the solubilization limit for PC is approached (approx. 2:1 PC:taurocholate), differential behavior is observed for the two components: the motion of taurocholate becomes preferentially restricted, while polar portions of the PC remain mobile until large multilayers predominate.     

Endogenous proteinases modulate the function of the β-adrenergic receptor-adenylate cyclase system

Photoaffinity labeling techniques have recently demonstrated that mammalian β₁- and β₂-adrenergic receptors reside on peptides of M_r 62 000–64 000. These receptor peptides are susceptible to endogenous metalloproteinases which produce peptides of M_r 30 000–55 000. Several proteinase inhibitors markedly attenuate this process, specifically EDTA and EGTA. In this study we investigated the functional significance of this proteolysis (and its inhibition) in the β₂-adrenergic receptor-adenylate cyclase system derived from rat lung membranes. Membrane preparations containing proteolytically derived fragments of the receptor of M_r 40000–55 000 are fully functional with respect to their ability to bind β-adrenergic antagonist radioligands such as [³H]dihydroalprenolol and β-adrenergic antagonist photoaffinity reagents such as p-azido-m-[^{125I]iodobenzylcarazolol}. They retain the ability to form a high-affinity, agonist-promoted, guanine nucleotide-sensitive complex thought to represent a ternary complex of agonist, receptor and guanine nucleotide regulatory protein. Nonetheless, after proteolysis, GTP is less able to revert this high-affinity receptor complex to one of lower affinity, and all aspects of adenylate cyclase stimulation are reduced. In addition, the functional integrity of the N protein in membranes prepared without proteinase inhibitors is reduced as assessed by reconstitution studies with the cyc[su− variant of S49 lymphoma cell membranes. These results suggest that endogenous proteolysis does not directly impair the ability of β-adrenergic receptors to either bind ligands or interact with the guanine nucleotide regulatory protein. However, they imply that endogenous proteolysis likely impairs the functionality of other components of the adenylate cyclase system, such as the nucleotide regulatory protein.     

Retinoblastoma,gross internal malformations,and deletion 13q14→q31

Summary A male patient with an interstitial deletion 13q14q31 is described. Our necropsy findings included a left retinoblastoma and several gross internal malformations. In this paper we reaffirm that band 13q14 is involved in cases of retinoblastoma and we propose, after studying accompanying cases of total or partial long arm trisomies 13, that the loss of specific 13q bands, from 13q14 to 13q31 is responsible for the congenital defects we are describing.     

Biogenesis of mitochondria 49 identification and mapping of a new mitochondrial locus (tsr1) which maps within polar region of yeast mitochondrial genome.

Summary An enrichment procedure which facilitates the isolation of conditional respiratory-deficient mutants of Saccharomyces cerevisiae is reported. Detailed genetic analysis of one mutant which exhibits a respiratory deficient phenotype at low temperature (18°C) is also presented. The phenotype is due to a single lesion at a new locus, tsr1, located on the mitochondrial DNA. By analysis of locus retention patterns in a set of physically characterized petite strains, the tsr1 mutation has been mapped within the segment 0–5 map units on the physical map of the yeast mitochondrial genome. This segment of the mitochondrial DNA also contains the cap1 and ery1 loci and the cistron for the mitochondrial 21S rRNA. Studies of the frequencies of co-retention of markers in petite populations, and of the frequencies of recombination of markers in non-polar crosses (⁺ × ⁺), demonstrate linkage of the tsr1 locus to both the cap1 and ery1 loci. The degree of linkage indicates that tsr1 is closer to the ery1 locus. Comparison of pairwise recombination frequencies for these three markers indicate the order cap1-tsr1-ery1. The tsr1 locus lies within the segment of the mitochondrial genome which is influenced by the polarity locus , and analysis of transmission and recombination frequencies and polarities in a polar (⁺ × ^-) cross show that the behaviour of the tsr1 locus is similar to that of ery1. However striking features of this cross are that the recombination frequency between tsr1 and ery1 is comparable to that observed in non-polar crosses, and that the polarity for recombination between tsr1 and cap1 or ery1 is extremely low.     

Studies on an Indian polydesmoid millipede Streptogonopus phipsoni Life cycle and swarming behaviour of the larvae

The adults of Streptogonopus phipsoni (Pocock), an Indian polydesmoid millipede, emerge from the soil at the onset of the monsoon and mate. Eggs are laid in the soil and the adults die. The larvae leave the soil at stadium III and, apart from moulting periods, remain on the surface until the end of the monsoon. The larvae are aggregated in swarms, usually consisting of several hundred individuals. They are active on open ground, including metalled roads, during daylight, but usually spend the night in an inactive state under cover of stones or vegetation. If a swarm is disturbed, the individuals scatter but later reaggregate.
Laboratory experiments show that the larvae are sensitive to light even though they lack eyes, and if given a choice spend more time in the light than the dark. Just before and after moulting however they spend more time in the dark than in the light.
Experiments were carried out on the reactions of the larvae to aquatic suspensions of benzaldeyde, since this substance is related to components of the exudate of the repugnatorial glands; strong concentrations (10^-1) repelled the larvae, whilst weak concentrations (10^-6) attracted them. It is suggested that swarms may be dispersed or reaggregated by the effects of variations in concentration of components of the exudates. The benefits to the larvae which may result from swarming are discussed.     

DNA polymerase activity in developmental stages of Drosophila melanogaster

An assay procedure was developed that allowed the first reproducible measurement of DNA polymerase activity in all developmental stages of Drosophila melanogaster. Evidence is presented that the same enzymatic species is present in extracts of embryos, pupae, and adults of both sexes and that this activity has many properties similar to vertebrate α-polymerases. Polymerase activity per individual is low in embryos and rises steadily through larval instars, reaches a peak in early pupae, declines through the late pupal period, and remains low in newly eclosed adults of both sexes. A dramatic increase is observed in adult females as mature oocytes are formed. This pattern of enzyme activity is completely coincident with changes in DNA levels during development, and suggests that the Drosophila enzyme, like vertebrate α-polymerases, functions in cellular DNA replication. Two mutagen-sensitive mutants, deficient in both replication on undamaged templates and postreplication repair, were found to have normal levels of this α-polymerase activity. Our results suggest that a single enzymatic species of α-polymerase holoenzyme exists in Drosophila and is common to all developmental stages of this organism.