55 research outputs found
Stability-activity tradeoffs constrain the adaptive evolution of RubisCO
A well-known case of evolutionary adaptation is that of ribulose-1,5-bisphosphate carboxylase (RubisCO), the enzyme responsible for fixation of CO2 during photosynthesis. Although the majority of plants use the ancestral C3 photosynthetic pathway, many flowering plants have evolved a derived pathway named C4 photosynthesis. The latter concentrates CO2, and C4 RubisCOs consequently have lower specificity for, and faster turnover of, CO2. The C4 forms result from convergent evolution in multiple clades, with substitutions at a small number of sites under positive selection. To understand the physical constraints on these evolutionary changes, we reconstructed in silico ancestral sequences and 3D structures of RubisCO from a large group of related C3 and C4 species. We were able to precisely track their past evolutionary trajectories, identify mutations on each branch of the phylogeny, and evaluate their stability effect. We show that RubisCO evolution has been constrained by stability-activity tradeoffs similar in character to those previously identified in laboratory-based experiments. The C4 properties require a subset of several ancestral destabilizing mutations, which from their location in the structure are inferred to mainly be involved in enhancing conformational flexibility of the open-closed transition in the catalytic cycle. These mutations are near, but not in, the active site or at intersubunit interfaces. The C3 to C4 transition is preceded by a sustained period in which stability of the enzyme is increased, creating the capacity to accept the functionally necessary destabilizing mutations, and is immediately followed by compensatory mutations that restore global stability
Fast Tuning Electronically Switched 16 x 1 Channel Receiver For Packet-Switched WDM Systems
This paper revisits an optical receiver topology, for a wavelength division multiplexing (WDM) optical network at 2.5 Gbps bit rate, based on non-tunable wavelength demultiplexing and electronic switching.We demonstrate novel, monolithically integrated, four-channel optical receiver module composed of MESFET transimpedance amplifiers and switches that can be independently switched âonâ or âoffâ electronically by a digital signal. The selector chips have also been reconfigured as a 16 channel selector array. Frequency and noise performance as well as switching speed and crosstalk between neighboring channels have been investigated
Trends di incidenza 1986-2001 del tumore del polmone e sua distribuzione per morfologia nella popolazione genovese.
Trends di incidenza del tumore del polmone - distribuzione per morfologia nella popolazione genoves
Sopravvivenza per il tumore della prostata in Italia.
Sopravvivenza per il tumore della prostat
"Trend di incidenza 1986-1997 dell'adenocarcinoma esofageo e gastrico nella popolazione genovese".
Trend incidenza adenocarcinoma esofageo e gastric
Lung and stomach cancer incidence trends in Ligurian Cancer Registry from 1986 to 1992.
Lung and stomach cancer incidence tren
Trend d\u2019incidenza e di sopravvivenza dei tumori del colon-retto per la citt\ue0 e l\u2019insieme degli altri comuni della provincia di Genova.
Trend d\u2019incidenza e di sopravvivenza dei tumori del colon-rett
Trends in incidenza 1986-97 del tumore polmonare per tipo morfologico.
Trends incidenza tumore polmonare per tipo morfologico
"Concordanza codifica: Registro Mortalit\ue0 Regione Liguria vs Registro Regione Liguria. Sedi: epato-bilio-pancreatiche e mal definite; area: comune di Genova."
Concordanza codifica: mortalit\ue0 vs Tumori. Sedi: epato-bilio-pancreatiche e mal definit
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