Lipid environment modulates processivity and kinetics of a presenilin homolog acting on multiple substrates in vitro.

Intramembrane proteases (IPs) hydrolyze peptides in the lipid membrane. IPs participate in a number of cellular pathways including immune response and surveillance, and cholesterol biosynthesis, and they are exploited by viruses for replication. Despite their broad importance across biology, how activity is regulated in the cell to control protein maturation and release of specific bioactive peptides at the right place and right time remains largely unanswered, particularly for the intramembrane aspartyl protease (IAP) subtype. At a molecular biochemical level, different IAP homologs can cleave non-biological substrates, and there is no sequence recognition motif among the nearly 150 substrates identified for just one IAP, presenilin-1, the catalytic component of γ-secretase known for its involvement in the production of amyloid-ß plaques associated with Alzheimer disease. Here we used gel-based assays combined with quantitative mass spectrometry and FRET-based kinetics assays to probe the cleavage profile of the presenilin homolog from the methanogen Methanoculleus marisnigri JR1 as a function of the surrounding lipid-mimicking environment, either detergent micelles or bicelles. We selected four biological IAP substrates that have not undergone extensive cleavage profiling previously, namely, the viral core protein of Hepatitis C virus, the viral core protein of Classical Swine Fever virus, the transmembrane segment of Notch-1, and the tyrosine receptor kinase ErbB4. Our study demonstrates a proclivity toward cleavage of substrates at positions of low average hydrophobicity and a consistent role for the lipid environment in modulating kinetic properties.

Overtime trend of thyroid hormones and thyroid autoimmunity and ovarian reserve: a longitudinal population study with a 12-year follow up.

BACKGROUND: Ovarian reserve, vital for reproductive function, can be adversely affected by thyroid diseases. Despite alternations of thyroid hormones with ageing, data on interactions between the overtime trend of thyroid functions and ovarian reserve status has rarely been reported. We aimed to examine the overtime trend of thyroid hormones, thyroid peroxidase antibody (TPO Ab) and their associations with ovarian reserve status, identified by levels of age specific anti-mullerian hormone (AMH) in reproductive aged women, who participated in 12-year cohort of Tehran Thyroid Study (TTS). METHODS: Reproductive age women(n = 775) without any thyroid disease or ovarian dysfunction were selected from the Tehran Thyroid Study cohort. Participants were divided into four age specific AMH quartiles (Q1-Q4), Q1, the lowest and Q4, the highest. AMH was measured at the initiation of study and thyroid stimulating hormone (TSH), free T4 (FT4), and TPO Ab were measured at baseline and at three follow up visits. RESULTS: At baseline, there was no statistically significant difference in thyroid hormones between women of the four quartiles, although TPO Ab levels were higher in women of Q1. During the follow ups, FT4 was decreased in all quartiles (p < 0.05), whereas TPO Ab increased in Q1 (p = 0.02). Odds ratio of overall TPO Ab positivity in women of Q1 was 2.08 fold higher than those in Q4. (OR: 2.08, 95%CI: 1.16, 3.72; p = 0.01). CONCLUSION: Women with the lowest ovarian reserves had higher levels of TPO Ab, with a positive trend of this antibody overtime in comparison to other quartiles, indicating that this group may be at a higher risk of hypothyroidism over time.

Zinc sulfide-chitosan hybrid nanoparticles as a robust surface for immobilization of Sillago sihama α-amylase.

In the present study, zinc sulfide-chitosan hybrid nanoparticles synthesized by chemical deposition were used as a matrix for the immobilization of purified α-amylase extracted from Sillago sihama (Forsskal, 1775). In this regard, the size and morphological structure of zinc sulfide-chitosan hybrid nanoparticles before and after the stabilization process were evaluated using FT-IR, DLS methods, as well as SEM and TEM electron microscopy, and EDS analyses. Then, the efficiency of the immobilized enzyme was measured in terms of temperature, optimal pH, stability at the critical temperature, and pH values. Immobilization of α-amylase on zinc sulfide -chitosan hybrid nanoparticles increased the long-term stability, as well as its endurance to critical temperatures and pH values; however, the optimal temperature and pH values of the enzyme were not altered following the immobilization process. The kinetic parameters of the enzyme were also changed during immobilization. Enzyme immobilization increased the Km, whereas decreased the catalytic efficiency (Kcat / Km) of the immobilized enzyme compared with the free enzyme. These results are very important as, in most cases, enzyme immobilization reduces the activity and catalytic efficiency of enzymes. The nano-enzyme produced in this study, due to its high temperature, and pH stability, could be a good candidate for industrial applications, especially in the food industry.