Chebychev Trajectory Optimization Program /CHEBYTOP/ Final report

Digital computer program for interplanetary trajectory optimization and variable thrust dat

Phosphorylation Provides a Negative Mode of Regulation for the Yeast Rab GTPase Sec4p

The Rab family of Ras-related GTPases are part of a complex signaling circuitry in eukaryotic cells, yet we understand little about the mechanisms that underlie Rab protein participation in such signal transduction networks, or how these networks are integrated at the physiological level. Reversible protein phosphorylation is widely used by cells as a signaling mechanism. Several phospho-Rabs have been identified, however the functional consequences of the modification appear to be diverse and need to be evaluated on an individual basis. In this study we demonstrate a role for phosphorylation as a negative regulatory event for the action of the yeast Rab GTPase Sec4p in regulating polarized growth. Our data suggest that the phosphorylation of the Rab Sec4p prevents interactions with its effector, the exocyst component Sec15p, and that the inhibition may be relieved by a PP2A phosphatase complex containing the regulatory subunit Cdc55p

Acetylation of RNA Polymerase II Regulates Growth-Factor-Induced Gene Transcription in Mammalian Cells

Lysine acetylation regulates transcription by targeting histones and nonhistone proteins. Here we report that the central regulator of transcription, RNA polymerase II, is subject to acetylation in mammalian cells. Acetylation occurs at eight lysines within the C-terminal domain (CTD) of the largest polymerase subunit and is mediated by p300/KAT3B. CTD acetylation is specifically enriched downstream of the transcription start sites of polymerase-occupied genes genome-wide, indicating a role in early stages of transcription initiation or elongation. Mutation of lysines or p300 inhibitor treatment causes the loss of epidermal growth-factor-induced expression of c-Fos and Egr2, immediate-early genes with promoter-proximally paused polymerases, but does not affect expression or polymerase occupancy at housekeeping genes. Our studies identify acetylation as a new modification of the mammalian RNA polymerase II required for the induction of growth factor response genes

Mechanoenzymatics of titin kinase

Biological responses to mechanical stress require strain-sensing molecules, whose mechanically induced conformational changes are relayed to signaling cascades mediating changes in cell and tissue properties. In vertebrate muscle, the giant elastic protein titin is involved in strain sensing via its C-terminal kinase domain (TK) at the sarcomeric M-band and contributes to the adaptation of muscle in response to changes in mechanical strain. TK is regulated in a unique dual autoinhibition mechanism by a C-terminal regulatory tail, blocking the ATP binding site, and tyrosine autoinhibition of the catalytic base. For access to the ATP binding site and phosphorylation of the autoinhibitory tyrosine, the C-terminal autoinhibitory tail needs to be removed. Here, we use AFM-based single-molecule force spectroscopy, molecular dynamics simulations, and enzymatics to study the conformational changes during strain-induced activation of human TK. We show that mechanical strain activates ATP binding before unfolding of the structural titin domains, and that TK can thus act as a biological force sensor. Furthermore, we identify the steps in which the autoinhibition of TK is mechanically relieved at low forces, leading to binding of the cosubstrate ATP and priming the enzyme for subsequent autophosphorylation and substrate turnover