Differential effects of co-chaperonin homologs on cpn60 oligomers.

In this study, we have investigated the relationship between chaperonin/co-chaperonin binding, ATP hydrolysis, and protein refolding in heterologous chaperonin systems from bacteria, chloroplast, and mitochondria. We characterized two types of chloroplast cpn60 oligomers, ch-cpn60 composed of alpha and beta subunits (alpha(7)beta(7) ch-cpn60) and one composed of all beta subunits (beta(14) ch-cpn60). In terms of ATPase activity, the rate of ATP hydrolysis increased with protein concentration up to 60 microM, reflecting a concentration at which the oligomers are stable. At high concentrations of cpn60, all cpn10 homologs inhibited ATPase activity of alpha(7)beta(7) ch-cpn60. In contrast, ATPase of beta(14) ch-cpn60 was inhibited only by mitochondrial cpn10, supporting previous reports showing that beta(14) is functional only with mitochondrial cpn10 and not with other cpn10 homologs. Surprisingly, direct binding assays showed that both ch-cpn60 oligomer types bind to bacterial, mitochondrial, and chloroplast cpn10 homologs with an equal apparent affinity. Moreover, mitochondrial cpn60 binds chloroplast cpn20 with which it is not able to refold denatured proteins. Protein refolding experiments showed that in such instances, the bound protein is released in a conformation that is not able to refold. The presence of glycerol, or subsequent addition of mitochondrial cpn10, allows us to recover enzymatic activity of the substrate protein. Thus, in our systems, the formation of co-chaperonin/chaperonin complexes does not necessarily lead to protein folding. By using heterologous oligomer systems, we are able to separate the functions of binding and refolding in order to better understand the chaperonin mechanism.

The changing pattern of consanguinity in a selected region of the Israeli Arab community.

The prevalence of consanguinity within the Israeli Arab community is relatively high, and is associated with high rates of inherited disorders that lead to a high frequency of morbidity and mortality. Data on consanguinity between couples were recorded during two periods (1980-1985 and 2000-2004) in relation to socioeconomic status of 4 selected villages. Two of the villages (A and B) are known to have high socioeconomic status, and the other two (C and D) are known to have low socioeconomic status. The average incidence of consanguineous marriages has slightly decreased from 33.1% in the first period to 25.9% in the second period (P = 0.0218) in all of the 4 villages. Marriages between first cousins showed a more significant decrease, from 23.9% in the first period to 13.6% in the second period (P < 0.0001). The average consanguinity rates of villages A and B were found to decrease from 22.3 to 16.2% respectively (P < 0.001) between the two observation periods, whereas those of villages C and D were found to decrease from 42.3 to 37.2%, (P < 0.001) during the same two periods. Thus, there has been a change in the pattern of consanguinity within the selected Israeli Arab villages, between the two study periods. This change seems to correlate with the sociodemographic status of the villages. Therefore, improving the socioeconomic status of the villages, as well as implementation of proper health education programs, is expected to have a positive effect in reducing consanguinity.

On the oligomeric state of chloroplast chaperonin 10 and chaperonin 20.

Type I chaperonins are fundamental protein folding machineries that function in eubacteria, mitochondria and chloroplasts. Eubacteria and mitochondria contain chaperonin systems comprised of homo-oligomeric chaperonin 60 tetradecamers and co-chaperonin 10 heptamers. In contrast, the chloroplast chaperonins are heterooligomeric tetradecamers that are composed of two subunit types, alpha and beta. Additionally, chloroplasts contain two structurally distinct co-chaperonins. One, ch-cpn10, is probably similar to the mitochondrial and bacterial co-chaperonins, and is composed of 10 kDa subunits. The other, termed ch-cpn20 is composed of two cpn10-like domains that are held together by a short linker. While the oligomeric structure of ch-cpn10 remains to be elucidated, it was previously suggested that ch-cpn20 forms tetramers in solution, and that this is the functional oligomer. In the present study, we investigated the properties of purified ch-cpn10 and ch-cpn20. Using bifunctional cross-linking reagents, gel filtration chromatography and analytical ultracentrifugation, we show that ch-cpn10 is a heptamer in solution. In contrast, ch-cpn20 forms multiple oligomers that are in dynamic equilibrium with each other and cover a broad spectrum of molecular weights in a concentration-dependent manner. However, upon association with GroEL, only one type of co-chaperonin-GroEL complex is formed.