The bacterial SRP receptor, FtsY, is activated on binding to the translocon.

Proteins are inserted into the bacterial plasma membrane cotranslationally after translating ribosomes are targeted to the translocon in the membrane via the signal recognition particle (SRP) pathway. The targeting pathway involves an interaction between SRP and the SRP receptor, FtsY. Here we focus on the role of FtsY and its interaction with the translocon in controlling targeting. We show that in unbound FtsY the NG and A domains interact with one another. The interaction involves the membrane-targeting region at the junction between A and N domain. The closed form of FtsY is impaired in binding to SRP. Upon binding to the phospholipid-embedded translocon the domains of FtsY move apart. This enhances the docking of the FtsY NG domain to the homologous NG domain of the SRP protein Ffh. Thus, FtsY binding to the translocon has a central role in orchestrating the formation of a quaternary transfer complex in which the nascent peptide is transferred to the translocon. We propose that FtsY activation at the translocon ensures that ribosome-SRP complexes are directed to available translocons. This way sequestering SRP in futile complexes with unbound FtsY can be avoided and efficient targeting to the translocon achieved.

Electrostatics and Intrinsic Disorder Drive Translocon Binding of the SRP Receptor FtsY.

Integral membrane proteins in bacteria are co-translationally targeted to the SecYEG translocon for membrane insertion via the signal recognition particle (SRP) pathway. The SRP receptor FtsY and its N-terminal A domain, which is lacking in any structural model of FtsY, were studied using NMR and fluorescence spectroscopy. The A domain is mainly disordered and highly flexible; it binds to lipids via its N terminus and the C-terminal membrane targeting sequence. The central A domain binds to the translocon non-specifically and maintains disorder. Translocon targeting and binding of the A domain is driven by electrostatic interactions. The intrinsically disordered A domain tethers FtsY to the translocon, and because of its flexibility, allows the FtsY NG domain to scan a large area for binding to the NG domain of ribosome-bound SRP, thereby promoting the formation of the quaternary transfer complex at the membrane.

Lateral opening of the bacterial translocon on ribosome binding and signal peptide insertion.

Proteins are co-translationally inserted into the bacterial plasma membrane via the SecYEG translocon by lateral release of hydrophobic transmembrane segments into the phospholipid bilayer. The trigger for lateral opening of the translocon is not known. Here we monitor lateral opening by photo-induced electron transfer (PET) between two fluorophores attached to the two SecY helices at the rim of the gate. In the resting translocon, the fluorescence is quenched, consistent with a closed conformation. Ribosome binding to the translocon diminishes PET quenching, indicating opening of the gate. The effect is larger with ribosomes exposing hydrophobic transmembrane segments and vanishes at low temperature. We propose a temperature-dependent dynamic equilibrium between closed and open conformations of the translocon that is shifted towards partially and fully open by ribosome binding and insertion of a hydrophobic peptide, respectively. The combined effects of ribosome and peptide binding allow for co-translational membrane insertion of successive transmembrane segments.

Interplay between trigger factor and other protein biogenesis factors on the ribosome.

Nascent proteins emerging from translating ribosomes in bacteria are screened by a number of ribosome-associated protein biogenesis factors, among them the chaperone trigger factor (TF), the signal recognition particle (SRP) that targets ribosomes synthesizing membrane proteins to the membrane and the modifying enzymes, peptide deformylase (PDF) and methionine aminopeptidase (MAP). Here, we examine the interplay between these factors both kinetically and at equilibrium. TF rapidly scans the ribosomes until it is stabilized on ribosomes presenting TF-specific nascent chains. SRP binding to those complexes is strongly impaired. Thus, TF in effect prevents SRP binding to the majority of ribosomes, except those presenting SRP-specific signal sequences, explaining how the small amount of SRP in the cell can be effective in membrane targeting. PDF and MAP do not interfere with TF or SRP binding to translating ribosomes, indicating that nascent-chain processing can take place before or in parallel with TF or SRP binding.

Dynamic switch of the signal recognition particle from scanning to targeting.

Ribosomes synthesizing inner membrane proteins in Escherichia coli are targeted to the membrane by the signal recognition particle (SRP) pathway. By rapid kinetic analysis we show that after initial binding to the ribosome, SRP undergoes dynamic fluctuations in search of additional interactions. Non-translating ribosomes, or ribosomes synthesizing non-membrane proteins, do not provide these contacts, allowing SRPs to dissociate rapidly. A nascent peptide in the exit tunnel stabilizes SRPs in a standby state. Binding to the emerging signal-anchor sequence (SAS) of a nascent membrane protein halts the fluctuations of SRP, resulting in complex stabilization and recruitment of the SRP receptor. We propose a kinetic model where SRP rapidly scans all ribosomes until it encounters a ribosome exposing an SAS. Binding to the SAS switches SRP into the targeting mode, in which dissociation is slow and docking of the SRP receptor is accelerated.

A United Nations General Assembly Special Session for mental, neurological, and substance use disorders: the time has come.

Mental, neurological, and substance use (MNS) disorders are leading causes of the global burden of disease and profoundly impact the social and economic well-being of individuals and communities. The majority of people affected by MNS disorders globally do not have access to evidence-based interventions and many experience discrimination and abuses of their human rights. A United Nations General Assembly Special Session (UNGASS) is needed to focus global attention on MNS disorders as a core development issue requiring commitments to improve access to care, promote human rights, and strengthen the evidence on effective prevention and treatment.

Trends in mental health and substance abuse services at the nation's community health centers: 1998-2003.

OBJECTIVE: We examined trends in delivery of mental health and substance abuse services at the nation's community health centers. METHODS: Analyses used data from the Health Resources and Services Administration (HRSA), Bureau of Primary Care's (BPHC) 1998 and 2003 Uniform Data System, merged with county-level data. RESULTS: Between 1998 and 2003, the number of patients diagnosed with a mental health/substance abuse disorder in community health centers increased from 210,000 to 800,000. There was an increase in the number of patients per specialty mental health/substance abuse treatment provider and a decline in the mean number of patient visits, from 7.3 visits per patient to 3.5 by 2003. Although most community health centers had some on-site mental health/substance abuse services, centers without on-site services were more likely to be located in counties with fewer mental health/substance abuse clinicians, psychiatric emergency rooms, and inpatient hospitals. CONCLUSIONS: Community health centers are playing an increasingly central role in providing mental health/substance abuse treatment services in the United States. It is critical both to ensure that these centers have adequate resources for providing mental health/substance abuse care and that they develop effective linkages with mental health/substance abuse clinicians in the communities they serve.

Signal sequence-independent membrane targeting of ribosomes containing short nascent peptides within the exit tunnel.

Ribosomes synthesizing inner membrane proteins in Escherichia coli are targeted to the translocon in the plasma membrane by the signal recognition particle (SRP) and the SRP receptor, FtsY. Here we show using a purified system that membrane targeting does not require an exposed signal-anchor sequence, as SRP-dependent targeting takes place with ribosomes containing short nascent peptides, with or without a signal-anchor sequence, within the peptide exit tunnel. Signaling from inside the tunnel involves ribosomal protein L23, which constitutes part of the SRP binding site. When nascent peptides emerge from the ribosome, the targeting complex is maintained with ribosomes exposing a signal-anchor sequence, whereas ribosomes exposing other sequences are released. These results indicate that ribosome-nascent chain complexes containing any nascent peptide within the exit tunnel can enter the SRP targeting pathway to be sorted at the membrane into ribosome-nascent chain complexes that synthesize either membrane or cytosolic proteins.

Trends in Mental Health and Substance Abuse Services at the Nation's Community Health Centers: 1998-2003.

OBJECTIVE: We examined trends in delivery of mental health and substance abuse services at the nation's community health centers. METHODS: Analyses used data from the Health Resources and Services Administration (HRSA), Bureau of Primary Care's (BPHC) 1998 and 2003 Uniform Data System, merged with county-level data. RESULTS: Between 1998 and 2003, the number of patients diagnosed with a mental health/substance abuse disorder in community health centers increased from 210,000 to 800,000. There was an increase in the number of patients per specialty mental health/substance abuse treatment provider and a decline in the mean number of patient visits, from 7.3 visits per patient to 3.5 by 2003. Although most community health centers had some on-site mental health/substance abuse services, centers without on-site services were more likely to be located in counties with fewer mental health/substance abuse clinicians, psychiatric emergency rooms, and inpatient hospitals. CONCLUSIONS: Community health centers are playing an increasingly central role in providing mental health/substance abuse treatment services in the United States. It is critical both to ensure that these centers have adequate resources for providing mental health/substance abuse care and that they develop effective linkages with mental health/substance abuse clinicians in the communities they serve.

The Carter Center Mental Health Program: addressing the public health crisis in the field of mental health through policy change and stigma reduction.

Some of the most pervasive and debilitating illnesses are mental illnesses, according to World Health Organization's The World Health Report 2001--Mental Health: New Understanding, New Hope. Neuropsychiatric conditions account for four of the top five leading causes of years of life lived with disability in people aged 15 to 44 in the Western world. Many barriers prevent people with mental illnesses from seeking care, such as prohibitive costs, lack of insurance, and the stigma and discrimination associated with mental illnesses. The Carter Center Mental Health Program, established in 1991, focuses on mental health policy issues within the United States and internationally. This article examines the public health crisis in the field of mental health and focuses on The Carter Center Mental Health Program's initiatives, which work to increase public knowledge of and decrease the stigma associated with mental illnesses through their four strategic goals: reducing stigma and discrimination against people with mental illnesses; achieving equity of mental health care comparable with other health services; advancing early promotion, prevention, and early intervention services for children and their families; and increasing public awareness about mental illnesses and mental health issues.

A survey of mental health leaders one year after the President's New Freedom Commission report.

As part of the 19th annual Rosalynn Carter Symposium on Mental Health Policy, held in 2003, an anonymous online survey of symposium participants was conducted to gain insight into participants' perceptions of the impact on their organizations of the President's New Freedom Commission and its recommendations. The participants were national mental health leaders representing a broad range of mental health agencies and organizations. The results of the survey suggest that the New Freedom Commission has had a substantial impact on the organizations represented at the symposium. Findings on successes and challenges in implementing the recommendations suggest areas for ongoing efforts to transform mental health care.