Nieman, M. | Search bioRxiv

bioRxiv2024

The Plasmodium falciparum NCR1 membrane protein is a novel antimalarial target that exports cholesterol to maintain membrane homeostasis

Malaria is an extremely devastating parasitic infection that kills over half a million people each year. It is the leading cause of death in many developing countries, in part, due to a lack of resources and readily available therapeutics. Unfortunately, the most prevalent and deadliest causative agent of malaria, Plasmodium falciparum, has developed resistance to nearly all currently available antimalarial drugs. The P. falciparum Niemann-Pick Type C1-related (PfNCR1) transporter has been identified as a druggable target, as it is required for membrane homeostasis of the parasite. However, the structure and detailed molecular mechanism of this membrane protein are not yet available. Here we present three structures of PfNCR1 both in the absence and presence of the functional inhibitor MMV009108 at resolutions between 2.98 [A] and 3.81 [A] using single-particle cryo-electron microscopy (cryo-EM). The data suggest that PfNCR1 binds cholesterol and forms a cholesterol transport tunnel to modulate the composition of the parasite plasma membrane. Cholesterol efflux assays substantiate this as they show that PfNCR1 is an exporter capable of extruding cholesterol from the membrane. Additionally, the inhibition mechanism of MMV009108 appears to be due to a direct blockage of PfNCR1, preventing this transporter from shuttling cholesterol.

biochemistry↗

bioRxiv2024

Fast skeletal myosin binding protein-C expression exacerbates dysfunction in heart failure

During heart failure, gene and protein expression profiles undergo extensive compensatory and pathological remodeling. We previously observed that fast skeletal myosin binding protein-C (fMyBP-C) is upregulated in diseased mouse hearts. While fMyBP-C shares significant homology with its cardiac paralog, cardiac myosin binding protein-C (cMyBP-C), there are key differences that may affect cardiac function. However, it is unknown if the expression of fMyBP-C expression in the heart is a pathological or compensatory response. We aim to elucidate the cardiac consequence of either increased or knockout of fMyBP-C expression. To determine the sufficiency of fMyBP-C to cause cardiac dysfunction, we generated cardiac-specific fMyBP-C over-expression mice. These mice were further crossed into a cMyBP-C null model to assess the effect of fMyBP-C in the heart in the complete absence of cMyBP-C. Finally, fMyBP-C null mice underwent transverse aortic constriction (TAC) to define the requirement of fMyBP-C during heart failure development. We confirmed the upregulation of fMyBP-C in several models of cardiac disease, including the use of lineage tracing. Low levels of fMyBP-C caused mild cardiac remodeling and sarcomere dysfunction. Exclusive expression of fMyBP-C in a heart failure model further exacerbated cardiac pathology. Following 8 weeks of TAC, fMyBP-C null mice demonstrated greater protection against heart failure development. Mechanistically, this may be due to the differential regulation of the myosin super-relaxed state. These findings suggest that the elevated expression of fMyBP-C in diseased hearts is a pathological response. Targeted therapies to prevent upregulation of fMyBP-C may prove beneficial in the treatment of heart failure. Significance StatementRecently, the sarcomere - the machinery that controls heart and muscle contraction - has emerged as a central target for development of cardiac therapeutics. However, there remains much to understand about how the sarcomere is modified in response to disease. We recently discovered that a protein normally expressed in skeletal muscle, is present in the heart in certain settings of heart disease. How this skeletal muscle protein affects the function of the heart remained unknown. Using genetically engineered mouse models to modulate expression of this skeletal muscle protein, we determined that expression of this skeletal muscle protein in the heart negatively affects cardiac performance. Importantly, deletion of this protein from the heart could improve heart function suggesting a possible therapeutic avenue.

physiology↗