Dis-assembly lines: the proteasome and related ATPase-assisted proteases

Self-compartmentalizing proteases, such as the proteasome and several prokaryotic energy-dependent proteases, are designed to act in the crowded environment of the cell. Proteins destined for degradation are recognized and unfolded by regulatory subcomplexes that invariably contain ATPase modules, before being translocated into another subcomplex, the proteolytic core, for degradation. The sequential actions effected on substrates are reflected in the linear arrangement of these subcomplexes; thus, the holocomplexes are organized as molecular disassembly and degradation lines.     

1,4-Dihydroindeno[1,2-c]pyrazoles as novel multitargeted receptor tyrosine kinase inhibitors

A series of 1,4-dihydroindeno[1,2-c]pyrazoles with a 3-thiophene substituent carrying a urea-type side chain were identified as potent multitargeted (VEGFR and PDGFR families) receptor tyrosine kinase inhibitors. A KDR homology model suggested that the urea moiety is able to interact with a recognition motif in the hydrophobic specificity pocket of the enzyme.     

Formation of cristae and crista junctions in mitochondria depends on antagonism between Fcj1 and Su e/g

Crista junctions (CJs) are important for mitochondrial organization and function, but the molecular basis of their formation and architecture is obscure. We have identified and characterized a mitochondrial membrane protein in yeast, Fcj1 (formation of CJ protein 1), which is specifically enriched in CJs. Cells lacking Fcj1 lack CJs, exhibit concentric stacks of inner membrane in the mitochondrial matrix, and show increased levels of F₁F_O–ATP synthase (F₁F_O) supercomplexes. Overexpression of Fcj1 leads to increased CJ formation, branching of cristae, enlargement of CJ diameter, and reduced levels of F₁F_O supercomplexes. Impairment of F₁F_O oligomer formation by deletion of its subunits e/g (Su e/g) causes CJ diameter enlargement and reduction of cristae tip numbers and promotes cristae branching. Fcj1 and Su e/g genetically interact. We propose a model in which the antagonism between Fcj1 and Su e/g locally modulates the F₁F_O oligomeric state, thereby controlling membrane curvature of cristae to generate CJs and cristae tips.     

Relevance of lysine snorkeling in the outer transmembrane domain of small viral potassium ion channels

Transmembrane domains (TMDs) are often flanked by Lys or Arg because they keep their aliphatic parts in the bilayer and their charged groups in the polar interface. Here we examine the relevance of this so-called "snorkeling" of a cationic amino acid, which is conserved in the outer TMD of small viral K(+) channels. Experimentally, snorkeling activity is not mandatory for Kcv(PBCV-1) because K29 can be replaced by most of the natural amino acids without any corruption of function. Two similar channels, Kcv(ATCV-1) and Kcv(MT325), lack a cytosolic N-terminus, and neutralization of their equivalent cationic amino acids inhibits their function. To understand the variable importance of the cationic amino acids, we reanalyzed molecular dynamics simulations of Kcv(PBCV-1) and N-terminally truncated mutants; the truncated mutants mimic Kcv(ATCV-1) and Kcv(MT325). Structures were analyzed with respect to membrane positioning in relation to the orientation of K29. The results indicate that the architecture of the protein (including the selectivity filter) is only weakly dependent on TMD length and protonation of K29. The penetration depth of Lys in a given protonation state is independent of the TMD architecture, which leads to a distortion of shorter proteins. The data imply that snorkeling can be important for K(+) channels; however, its significance depends on the architecture of the entire TMD. The observation that the most severe N-terminal truncation causes the outer TMD to move toward the cytosolic side suggests that snorkeling becomes more relevant if TMDs are not stabilized in the membrane by other domains.     

Somatostatin receptor subtype 1 modulates basal inhibition of growth hormone release in somatotrophs

Somatostatin (SST) inhibits the secretion of many peptide hormones including growth hormone (GH). The various functions of SST are mediated through at least five different receptor subtypes (SSTR1-5), their precise physiological roles have not been solved yet. Here we report on studies concerning the functional role of SSTR1 in the modulation of GH release from somatotrophs. Primary cell cultures from pituitaries of wild-type SSTR1 mice exposed to the SSTR1 selective somatostatin analog CH-275 show reduction of basal levels of GH secretion whereas somatotrophs isolated from SSTR1 null mutant mice did not respond to the agonist-mediated effect. This suggests that SSTR1 is involved in modulating basal GH levels in primary pituitary cell cultures and, together with SSTR2, may control the secretion of GH in the body.     

Identification of amides derived from 1H-pyrazolo[3,4-b]pyridine-5-carboxylic acid as potent inhibitors of human nicotinamide phosphoribosyltransferase (NAMPT)

Potent, 1H-pyrazolo[3,4-b]pyridine-containing inhibitors of the human nicotinamide phosphoribosyltransferase (NAMPT) enzyme were identified using structure-based design techniques. Many of these compounds exhibited nanomolar antiproliferation activities against human tumor lines in in vitro cell culture experiments, and a representative example (compound 26) demonstrated encouraging in vivo efficacy in a mouse xenograft tumor model derived from the A2780 cell line. This molecule also exhibited reduced rat retinal exposures relative to a previously studied imidazo-pyridine-containing NAMPT inhibitor. Somewhat surprisingly, compound 26 was only weakly active in vitro against mouse and monkey tumor cell lines even though it was a potent inhibitor of NAMPT enzymes derived from these species. The compound also exhibited only minimal effects on in vivo NAD levels in mice, and these changes were considerably less profound than those produced by an imidazo-pyridine-containing NAMPT inhibitor. The crystal structures of compound 26 and the corresponding PRPP-derived ribose adduct in complex with NAMPT were also obtained.     

Molecular ruler of tripeptidylpeptidase II: mechanistic principle of exopeptidase selectivity

The structure of tripeptidylpeptidase II (TPPII) has shown that it belongs to the group of exopeptidases which use a double-Glu motif to convey aminopeptidase activity. TPPII has been implicated in vital biological processes. At least one of these, antigen processing, requires the involvement of its endopeptidase activity. In order to understand the extent and molecular basis of this unusual functional promiscuity we have performed a systematic kinetic analysis of wild type Drosophila melanogaster TPPII and five point mutants of the double-Glu-motif (E312/E343) involving natural substrates. Unlike the known double-Glu motives of other exopeptidases, the double-Glu motif of TPPII is distinctly asymmetrical: E312 is the crucial determinant of the aminotripeptidolytic ruler mechanism. It both blocks the active-site cleft at substrate position P4 and forms a salt bridge with the N-terminus of the substrate. In contrast, E343 forms a much weaker salt bridge than E312 and it does not have a blocking role. An endopeptidase substrate can bind at relatively high affinity if the length of the substrate permits binding to several S′ sites. However, the lacking alignment of the substrate by the double-Glu motif causes the endopeptidolytic K_cat/K_M of TPPII to be very low.     

The Real World Mental Health Needs of Heart Failure Patients Are Not Reflected by the Depression Randomized Controlled Trial Evidence

Introduction

International depression screening guidelines in heart failure (HF) are partly based on depression treatment efficacy from randomized controlled trials (RCTs). Our aim was to test the external validity of depression RCT criteria in a sample of real-world HF patients.

Methods

HF patients admitted to 3 hospitals in South Australia were referred to a HF psychologist if not already receiving current psychiatric management by psychologist or psychiatrist elsewhere. Screening and referral protocol consisted of the following; (a). Patient Health Questionnaire ≥10; (b). Generalized Anxiety Disorder Questionnaire ≥7); (c). positive response to 1 item panic attack screener; (d). evidence of suicidality. Patients were evaluated against the most common RCT exclusion criteria personality disorder, high suicide risk, cognitive impairment, psychosis, alcohol or substance abuse or dependency, bi-polar depression.

Results

Total 81 HF patients were referred from 404 HF admissions, and 73 were assessed (age 60.6±13.4, 47.9% female). Nearly half (47%) met at least 1 RCT exclusion criterion, most commonly personality disorder (28.5%), alcohol/substance abuse (17.8%) and high suicide risk (11.0%). RCT ineligibility criteria was more frequent among patients with major depression (76.5% vs. 46.2%, p<.01) and dysthymia (26.5% vs. 7.7%, p = .03) but not significantly associated with anxiety disorders. RCT ineligible patients reported greater severity of depression (M = 16.6±5.0 vs. M = 12.9±7.2, p = .02) and were higher consumers of HF psychotherapy services (M = 11.5±4.7 vs. M = 8.5±4.8, p = .01).

Conclusion

In this real-world sample comparable in size to recent RCT intervention arms, patients with depression disorders presented with complex psychiatric needs including comorbid personality disorders, alcohol/substance use and suicide risk. These findings suggest external validity of depression screening and RCTs could serve as a basis for level A guideline recommendations in cardiovascular diseases.