The crystal structure of human procathepsin K

Cathepsin K is a cysteine protease present in human osteoclasts that plays an important role in bone resorption. Cathepsin K is synthesized as an inactive proenzyme and activated under conditions of low pH. Autoproteolytic processing of the N-terminal 99 amino acid propeptide produces the active, mature form of cathepsin K. It is presumed that the activation of procathepsin K in vivo occurs in the bone resorption pit, which has a low-pH environment. We have determined the structure of human procathepsin K at 2.8 A resolution. The structure of the mature enzyme domain within procathepsin K is virtually identical to that of mature cathepsin K. The fold of the propeptide of procathepsin K is similar to that observed in procathepsins B and L despite differences in length and sequence. A portion of the propeptide occupies the active site cleft of cathepsin K. Hydrophobic interactions, salt bridges, and hydrogen-bonding interactions are observed in the structure of the propeptide and between the propeptide and the mature enzyme of procathepsin K. These interactions suggest an explanation for the stability of the proenzyme. The structure of procathepsin K contributes to an understanding of the molecular basis of inhibition by the propeptide portion of the molecule and activation of this important member of the cysteine protease family.     

Selected subunits of the cytosolic chaperonin associate with microtubules assembled in vitro

The molecular chaperone activities of the only known chaperonin in the eukaryotic cytosol (cytosolic chaperonin containing T-complex polypeptide 1 (CCT)) appear to be relatively specialized; the main folding substrates in vivo and in vitro are identified as tubulins and actins. CCT is unique among chaperonins in the complexity of its hetero-oligomeric structure, containing eight different, although related, gene products. In addition to their known ability to bind to and promote correct folding of newly synthesized and denatured tubulins, we show here that CCT subunits alpha, gamma, zeta, and theta also associated with in vitro assembled microtubules, i.e. behaved as microtubule-associated proteins. This nucleotide-dependent association between microtubules and CCT polypeptides (Kd approximately 0.1 microM CCT subunit) did not appear to involve whole oligomeric chaperonin particles, but rather free CCT subunits. Removal of the tubulin COOH termini by subtilisin digestion caused all eight CCT subunits to associate with the microtubule polymer, thus highlighting the non-chaperonin nature of the selective CCT subunit association with normal microtubules.     

Psychological disorder and mortality in French older adults: do social relations modify the association?

The possible modifying effect of social relations on the association between depression and mortality was examined in a community-based cohort study. A total of 3,777 randomly selected persons 65 years of age and older in southwest France were followed over a 5-year period from 1988 in the Personnes Agees Quid (PAQUID). At study entry, the prevalence of elevated depressive symptomatology was 12.9% for men and 14.7% for women, and the reported relative isolation was 14.1% for men and 26.0% for women. During a total of 16,984 person-years of follow-up, 849 deaths occurred. Among participants with high levels of depressive symptomatology, the age-adjusted mortality rate ratio was 2.10 (95% confidence interval 1.7-2.7) in men and 1.76 (95% confidence interval 1.4-2.3) in women. When compared with individuals with the most connections, men and women with few social network connections were also at increased risk of mortality: age-adjusted rate ratio = 2.69 (95% confidence interval 1.9-3.8) for men and 1.56 (95% confidence interval 1.0-2.4) for women. Satisfaction with social support had a small but nonsignificant effect on mortality risk. For women, the excess risks due to depressive symptoms and few network connections are observed only in the 65- to 74-year age group, after adjusting for health and health behaviors. Social relations did not significantly modify the depression-mortality associations for either men or women, although the depression-mortality effect was reduced by 12.8% in men. The latter findings do not appear to be compatible with the buffering hypothesis, whereby we would expect social relations to decrease the depression-mortality association. Nonetheless, there are independent effects from these two factors, and older men who are depressed and not socially connected are at increased risk of dying earlier.     

T-cell activation: interplay at the interface

Recent studies have shown that, when a T cell interacts with a cognate antigen-presenting cell, an organized adhesive contact is formed between the two cells by a process which involves the dynamic, three-dimensional redistribution of entire signaling assemblies.     

Expression and secretion of Bacillus polymyxa neopullulanase in Saccharomyces cerevisiae

The relationship between concentration of 5-aminolevulinic acid in plasma (ALAP) and other biomarkers of lead exposure and effect was investigated in lead-exposed children. We measured ALAP by chemical derivatization and high-performance liquid chromatography with fluorescence detection. The study population consisted of 103 children: 78 from a referral clinic for children with lead poisoning and 25 from a general pediatric clinic. Blood lead concentration (PbB), age, and ALAP were higher in lead clinic subjects than in general clinic subjects. ALAP was significantly correlated with PbB (Spearman r=0.38, P=0.0007) and free erythrocyte protoporphyrin concentration (r=0.41, P=0.0002) in lead clinic subjects. PbB was a significant predictor of ALAP (P=0.0001) by multiple linear regression in all subjects. The average PbB in the 3- to 12-month period prior to blood collection correlated with ALAP to the same degree that current PbB correlated with ALAP. Possible associations between ALAP and adverse health outcomes, particularly neurobehavioral effects, should be investigated in children to assess the predictive value of ALAP for these endpoints.     

Coordinate intracellular expression of Salmonella genes induced during infection

Salmonella typhimurium in vivo-induced (ivi) genes were grouped by their coordinate behavior in response to a wide variety of environmental and genetic signals, including pH, Mg2+, Fe2+, and PhoPQ. All of the seven ivi fusions that are induced by both low pH and low Mg2+ (e.g., iviVI-A) are activated by the PhoPQ regulatory system. Iron-responsive ivi fusions include those induced under iron limitation (e.g., entF) as well as one induced by iron excess but only in the absence of PhoP (pdu). Intracellular expression studies showed that each of the pH- and Mg2+-responsive fusions is induced upon entry into and growth within three distinct mammalian cell lines: RAW 264.7 murine macrophages and two cultured human epithelial cell lines: HEp-2 and Henle-407. Each ivi fusion has a characteristic level of induction consistent within all three cell types, suggesting that this class of coordinately expressed ivi genes responds to general intracellular signals that are present both in initial and in progressive stages of infection and may reflect their responses to similar vacuolar microenvironments in these cell types. Investigation of ivi expression patterns reveals not only the inherent versatility of pathogens to express a given gene(s) at various host sites but also the ability to modify their expression within the context of different animal hosts, tissues, cell types, or subcellular compartments.