Ligand binding to receptor proteins functions in signal transduction.

cell signaling

Cells, whether unicellular organisms or cells within multicellular organisms, adjust to signals within their environment and communicate with other cells.

autocrine : cellular responses : combinatorial : contact-dependent signaling : cytokines : delay/rapidity : distance of signal : endocrine : environmental signals : evolution : histidine kinase : hormones : neuronal signaling : neurotransmitters : paracrine : prokaryote signaling : rapidity/delay : receptor proteins : receptors : regulator proteins : SH domains : signal termination : signaling distance : signal transduction

Receptors are molecules that receive signals by binding ligands, for which receptors have varying binding affinity. Signal transduction is the process of converting signals from one form to another, ultimately adjusting an intracellular process, as in metabolic regulation, or an intranuclear process, such as gene expression.

Signaling operates at various distances:
● contact signaling – particularly important in immune signaling and during development

signaling mediated by synthesized signal mediators
● autocrine – chemical mediators (cytokines, growth factors) that operate on the cell that produces the mediator [1, 2]

signaling mediated by secreted signal mediators
● paracrine – short-range
● endocrine – long-range via hormones

Neurons signal at long-range by virtue of their long axonal processes, but neurotransmitters released into the synaptic cleft operate at short-range, enabling rapid, precise signaling.

Speed of signaling is determined by:
● speed of production of the signal (synthesis of mediators)
● speed of delivery of signal mediators (delivery of mediators to target cells)
● speed of cellular response to the signal
● depolarization, impulse propagation, repolarization of nerve cells

Signals are terminated by:
● dissociation of mediator ligand from receptor
● absorption of mediator by neighboring target cells (neurotransmitters and other paracrine mediators)
● enzymatic destruction of mediators
● immobilization by adsorption of mediators in ECM or by binding to intracellular proteins

Signal transduction is usually performed by enzymes in association with second messengers. Signaling proteins operate in a combinatorial fashion within signaling networks, greatly extending the biological roles of individual proteins. The simplest such system comprises two components – a histidine kinase protein that receives a signal and transmits it, via phosphorelay, to a partner response-regulator protein. Protein domains and motif interactions display considerable flexibility, providing an obvious evolutionary advantage. For example, single amino acid substitutions alter the binding specificity of SH2 domains such that specificity can change quite rapidly, enabling formation of new signaling connections as metazoan organisms became more complex.

Environmental signals include mechanical stimuli (light, sound) and chemical stimuli. The origin of a biochemical stimulus may be the cell itself (autocrine), adjacent cells (paracrine), the plasma membrane of adjacent cells (contact inhibition), or distant cells (endocrine).

Neurotransmission incorporates interaction between neurotransmitters and specific receptor proteins. Cytokines mediate paracrine stimulation, and hormones mediate endocrine stimulation.

Cellular responses to signaling include:
● alterations in gene expression (transcription)
● alteration of electrophysiological charge
cellular cycling and reproduction
regulation of cellular metabolic processes
biosynthesis with or without secretion
● cellular growth
chemotaxis, migration, and, in multicellular organisms, extravasation
● initiation of immune and inflammatory responses
differentiation into cell lines or maturation of cell lines
cellular survival or apoptosis

Intracellular interactions in prokaryotes
Four kinds of cell interactions can be distinguished:
1) Transfer of a chemical signal from one cell to another. The variety of such transfers is presented in several examples.
2) Signaling by direct physical contact between two cell bodies, which may involve their surfaces or cell appendages, such as fibrils, pili, or flagella (bacterial flagella). Direct physical contact is often involved in cell swarming.
3) Syntrophic metabolism. Schink Syntrophism Among Prokaryotes.
4) Gene transfer from one cell to another.

bacterial interactionsconcentration gradientsion channelsprotein pumpsreceptor proteinsreceptor-mediated endocytosisGPCRsGPCR familieshormonesneurotransmissionNitric Oxideneuronal interconnectionsphosphotransfer-mediated signaling pathwaysProtein Kinase Signaling Networkssignaling gradients :

KEGG Encyclopedia : Pathway ABC transporters : Pathway Phosphotransferase system (PTS) : Pathway Two-component system : Pathway MAPK signaling pathway : Pathway Wnt signaling pathway : Pathway Notch signaling pathway : Pathway Hedgehog signaling pathway : Pathway TGF-beta signaling pathway : Pathway VEGF signaling pathway : Pathway Jak-STAT signaling pathway : Pathway Calcium signaling pathway : Pathway Phosphatidylinositol signaling system : Pathway mTOR signaling pathway : Pathway Neuroactive ligand-receptor interaction : Pathway Cytokine-cytokine receptor interaction : Pathway ECM-receptor interaction : Pathway Cell adhesion molecules (CAMs) : Orthology Transporters (+diseases) : Orthology Two-component system : Orthology Receptors and channels (+diseases) : Orthology Cytokines :
Orthology Cell adhesion molecules (CAMs) : Orthology CAM ligands : Orthology CD molecules :
Orthology GTP-binding proteins :

Labels: , , ,

... receiving visitors since 12/21/06