Genetic and Biochemical Approaches for In Vivo and In Vitro Assessment of Protein Oligomerization: The Ryanodine Receptor Case Study

Differential activity of the corticosteroidogenic enzymes in normal cycling women and women with polycystic ovary syndrome

The phenotypic complex of patients with definitive diagnosis of polycystic ovary syndrome may include patients with normal and high serum androgen levels. Patients with hyperandrogenemia seem to present higher risk of changes to the glucose and lipid metabolism and, eventually, of earlier development of cardiovascular diseases than normoandrogenemic patients or healthy women. From a laboratory and clinical point of view, it is important to check androgen levels in patients with polycystic ovary syndrome. The identification of partial insufficiency of a given corticosteroidogenic enzyme is also relevant to understand the physiopathology of androgen increase in polycystic ovary syndrome. Therefore, the present review analyzes the functions of the different enzymes involved in the ovary and adrenal steroidogenesis in normal cycling women and in patients with polycystic ovary syndrome. In addition, it emphasizes appropriate reason for investigating eventual enzyme deficiency to provide rationale for prescription and follow-up of women with polycystic ovary syndrome.

Association of cardiac myosin-binding protein-C with the ryanodine receptor channel - putative retrograde regulation?

The cardiac muscle ryanodine receptor-Ca²⁺ release channel (RyR2) constitutes the sarcoplasmic reticulum (SR) Ca²⁺ efflux mechanism that initiates myocyte contraction, while cardiac myosin-binding protein-C (cMyBP-C; also known as MYBPC3) mediates regulation of acto-myosin cross-bridge cycling. In this paper, we provide the first evidence for the presence of direct interaction between these two proteins, forming a RyR2-cMyBP-C complex. The C-terminus of cMyBP-C binds with the RyR2 N-terminus in mammalian cells and the interaction is not mediated by a fibronectin-like domain. Notably, we detected complex formation between both recombinant cMyBP-C and RyR2, as well as between the native proteins in cardiac tissue. Cellular Ca²⁺ dynamics in HEK293 cells is altered upon co-expression of cMyBP-C and RyR2, with lowered frequency of RyR2-mediated spontaneous Ca²⁺ oscillations, suggesting that cMyBP-C exerts a potential inhibitory effect on RyR2-dependent Ca²⁺ release. Discovery of a functional RyR2 association with cMyBP-C provides direct evidence for a putative mechanistic link between cytosolic soluble cMyBP-C and SR-mediated Ca²⁺ release, via RyR2. Importantly, this interaction may have clinical relevance to the observed cMyBP-C and RyR2 dysfunction in cardiac pathologies, such as hypertrophic cardiomyopathy.

Calsequestrin interacts directly with the cardiac ryanodine receptor luminal domain

Cardiac muscle contraction requires sarcoplasmic reticulum (SR) Ca²⁺ release mediated by the quaternary complex comprising the ryanodine receptor 2 (RyR2), calsequestrin 2 (CSQ2), junctin (encoded by ASPH) and triadin. Here, we demonstrate that a direct interaction exists between RyR2 and CSQ2. Topologically, CSQ2 binding occurs at the first luminal loop of RyR2. Co-expression of RyR2 and CSQ2 in a human cell line devoid of the other quaternary complex proteins results in altered Ca²⁺-release dynamics compared to cells expressing RyR2 only. These findings provide a new perspective for understanding the SR luminal Ca²⁺ sensor and its involvement in cardiac physiology and disease.