Differential sensitivity of Src-family kinases to activation by SH3 domain displacement

Src-family kinases (SFKs) are non-receptor protein-tyrosine kinases involved in a variety of signaling pathways in virtually every cell type. The SFKs share a common negative regulatory mechanism that involves intramolecular interactions of the SH3 domain with the PPII helix formed by the SH2-kinase linker as well as the SH2 domain with a conserved phosphotyrosine residue in the C-terminal tail. Growing evidence suggests that individual SFKs may exhibit distinct activation mechanisms dictated by the relative strengths of these intramolecular interactions. To elucidate the role of the SH3:linker interaction in the regulation of individual SFKs, we used a synthetic SH3 domain-binding peptide (VSL12) to probe the sensitivity of downregulated c-Src, Hck, Lyn and Fyn to SH3-based activation in a kinetic kinase assay. All four SFKs responded to VSL12 binding with enhanced kinase activity, demonstrating a conserved role for SH3:linker interaction in the control of catalytic function. However, the sensitivity and extent of SH3-based activation varied over a wide range. In addition, autophosphorylation of the activation loops of c-Src and Hck did not override regulatory control by SH3:linker displacement, demonstrating that these modes of activation are independent. Our results show that despite the similarity of their downregulated conformations, individual Src-family members show diverse responses to activation by domain displacement which may reflect their adaptation to specific signaling environments in vivo. © 2014 Moroco et al

Soil carbon and nitrogen changes under Douglas-fir with and without red alder

We sampled pure Douglas-fir (DF) [Pseudotsuga menziesii (Mirb.) Franco] end mixed red alder (Alnus rabra Bong.)(RA) and DF (RA/DF) stands in 1980 and in 1999 to investigate the influence of RA on soil C and N pools. In RA/DF plots with 25% RA, the soil N pool to a 45-cm depth increased significantly (P < 0.05) by 190 g N m(-2), corresponding to 10 g N m(-2) yr(-1) accretion: The average between treatment soil N difference in 1999 was 166 g m(-2), representing N accretion of 8.7 g m(-2) yr(-1). In pure DF plots, the soil N pool remained nearly constant. Resin N mineralization in RA/DF plots was about ten fold greater than on pure DF plots, but the enhanced resin N availability did not affect DF foliar N concentration. Temporal plot pairing was necessary within this landscape with high spatial variability to detect significant changes in soil N pools, and only large effects, such as N addition by RA, could be identified with statistical significance. Minimum detectable difference (MDD) estimates for mean total soil C differences in RA/DF plots showed that it would require about 30 more years of C accretion to detect differences at P < 0.05. Conversely, total soil N accretion in RA/DF plots was 28% greater than the MDD after 19 yr