In Escherichia coli, components of a signal recognition particle (SRP) and its receptor have been identified which appear to be essential for efficient translocation of several proteins. In this study we use cross‐linking to demonstrate that E. coli SRP interacts with a variety of nascent presecretory proteins and integral inner membrane proteins. Evidence is presented that the interaction is correlated with the hydrophobicity of the core region of the signal sequence and thereby with its ability to promote transport in vivo. A second E. coli component, which is identified as trigger factor, can be efficiently cross‐linked to all tested nascent chains derived from both secreted and cytosolic proteins. We propose that SRP and trigger factor act as secretion‐specific and general molecular chaperone respectively, early in protein synthesis.

Background: ORG27569 is an allosteric modulator of CB1. Results: Although ORG27569 inhibits G protein coupling, it induces CB1 high affinity agonist binding, receptor internalization, and downstream ERK phosphorylation. Conclusion: The ORG27569-induced activation of ERK via CB1 is G i protein-independent. Significance: This is the first case of CB1 allosteric ligand-biased signaling.

The identification and cloning of the two major cannabinoid (CB1 and CB2) receptors together with the discovery of their endogenous ligands in the late 80s and early 90s, resulted in a major effort aimed at understanding the mechanisms and physiological roles of the endocannabinoid system (ECS). Due to its expression and localization in the central nervous system (CNS), the CB1 receptor together with its endogenous ligands (endocannabinoids (eCB)) and the enzymes involved in their synthesis and degradation, has been implicated in multiple pathophysiological events ranging from memory deficits to neurodegenerative disorders among others. In this review, we will provide a general overview of the ECS with emphasis on the CB1 receptor in health and disease. We will describe our current understanding of the complex aspects of receptor signaling and trafficking, including the non-canonical signaling pathways such as those mediated by β-arrestins within the context of functional selectivity and ligand bias. Finally, we will highlight some of the disorders in which CB1 receptors have been implicated. Significant knowledge has been achieved over the last 30 years. However, much more research is still needed to fully understand the complex roles of the ECS, particularly in vivo and to unlock its true potential as a source of therapeutic targets.

SummaryThe Escherichia coli signal recognition particle (SRP) and trigger factor are cytoplasmic factors that interact with short nascent polypeptides of presecretory and membrane proteins produced in a heterologous in vitro translation system. In this study, we use an E. coli in vitro translation system in combination with bifunctional cross-linking reagents to investigate these interactions in more detail in a homologous environment. Using this approach, the direct interaction of SRP with nascent polypeptides that expose particularly hydrophobic targeting signals is demonstrated, suggesting that inner membrane proteins are the primary physiological substrate of the E. coli SRP. Evidence is presented that the overproduction of proteins that expose hydrophobic polypeptide stretches, titrates SRP. In addition, trigger factor is efficiently cross-linked to nascent polypeptides of different length and nature, some as short as 57 amino acid residues, indicating that it is positioned near the nascent chain exit site on the E. coli ribosome.

Prokaryotic proteins destined for transport out of the cytoplasm typically contain an N-terminal extension sequence, called the signal peptide, which is required for export. It is evident that many secretory proteins utilize a common export system, yet the signal sequences themselves display very little primary sequence homology. In attempting to understand how different signal peptides are able to promote protein secretion through the same pathway, the physical features of natural signal sequences have been extensively examined for similarities that might play a part in function. Experimental data have confirmed statistical analyses which highlighted dominant features of natural signal sequences in Escherichia coli: a net positive charge in the N-terminus increases efficiency of transport; the core region must maintain a threshold level of hydrophobicity within a range of length limitations; the central portion adopts an alpha-helical conformation in hydrophobic environments; and the signal cleavage region is ideally six residues long, with small side-chain amino acids in the -1 and -3 positions. This review focuses on the parallels between signal peptide physical features and their functions, which emerge when the results of a variety of experimental approaches are combined. The requirement for each property may be ascribed to a potential interaction that is critical for efficient protein export. The summation of the key physical features produces signal peptides with the flexibility to function in multiple roles in order to expedite secretion. In this way, nature has indeed evolved exquisitely tuned signal sequences.