Olfactomedin (OLF) domain-containing proteins play roles in fundamental cellular processes and have been implicated in disorders ranging from glaucoma, cancers and inflammatory bowel disorder, to attention deficit disorder and childhood obesity. We solved crystal structures of the OLF domain of myocilin (myoc-OLF), the best studied such domain to date. Mutations in myoc-OLF are causative in the autosomal dominant inherited form of the prevalent ocular disorder glaucoma. The structures reveal a new addition to the small family of five-bladed β-propellers. Propellers are most well known for their ability to act as hubs for protein-protein interactions, a function that seems most likely for myoc-OLF, but they can also act as enzymes. A calcium ion, sodium ion and glycerol molecule were identified within a central hydrophilic cavity that is accessible via movements of surface loop residues. By mapping familial glaucoma-associated lesions onto the myoc-OLF structure, three regions sensitive to aggregation have been identified, with direct applicability to differentiating between neutral and disease-causing non-synonymous mutations documented in the human population worldwide. Evolutionary analysis mapped onto the myoc-OLF structure reveals conserved and divergent regions for possible overlapping and distinctive functional protein-protein or protein-ligand interactions across the broader OLF domain family. While deciphering the specific normal biological functions, ligands and binding partners for OLF domains will likely continue to be a challenging long-term experimental pursuit, atomic detail structural knowledge of myoc-OLF is a valuable guide for understanding the implications of glaucoma-associated mutations and will help focus future studies of this biomedically important domain family.

Heme is an essential cofactor and signaling molecule required for virtually all aerobic life. However, excess heme is cytotoxic. Therefore, heme must be safely transported and trafficked from the site of synthesis in the mitochondria or uptake at the cell surface, to hemoproteins in most subcellular compartments. While heme synthesis and degradation are relatively well characterized, little is known about how heme is trafficked and transported throughout the cell. Herein, we review eukaryotic heme transport, trafficking, and mobilization, with a focus on factors that regulate bioavailable heme. We also highlight the role of gasotransmitters and small molecules in heme mobilization and bioavailability, and heme trafficking at the host-pathogen interface.

The glaucoma-associated olfactomedin domain of myocilin (myoc-OLF) is a recent addition to the growing list of disease-associated amyloidogenic proteins. Inherited, diseasecausing myocilin variants aggregate intracellularly instead of being secreted to the trabecular meshwork (TM), which is a scenario toxic to TM cells and leads to early onset of ocular hypertension, the major risk factor for glaucoma. Here we systematically structurally and biophysically dissected myoc-OLF to better understand its amyloidogenesis. Under mildly destabilizing conditions, wild-type myoc-OLF adopts non-native structures that readily fibrillize when incubated at a temperature just below the transition for tertiary unfolding. With buffers at physiological pH, two main end-point fibril morphologies are observed: (a) straight fibrils common to many amyloids and (b) unique micron-length, ~300 nm or larger diameter species that lasso oligomers, which also exhibit classical spectroscopic amyloid signatures. Three disease-causing variants investigated herein exhibit non-native tertiary structures under physiological conditions, leading to accelerated growth rates and a variety of fibril morphologies. In particular, the well-documented D380A variant, which lacks calcium, forms large circular fibrils. Two amyloid forming peptide stretches have been identified, one for each of the main fibril morphologies observed. Our study places myoc-OLF within the larger landscape of the amylome and provides insight into the diversity of myoc-OLF aggregation that plays a role in glaucoma pathogenesis.

Background:Myocilin is an extracellular protein linked to glaucoma but is of unknown structure and function. Results: The myocilin olfactomedin domain contains a buried calcium ion ligated by Asp-380. Conclusion:The myocilin olfactomedin domain binds calcium with an unprecedented ligand arrangement. Significance: The presence of calcium within the OLF domain provides new clues into normal myocilin function, myocilin glaucoma pathogenesis, and biomedically important olfactomedin domains.

Glaucoma, a heterogeneous ocular disorder affecting ~60 million people worldwide, is characterized by painless neurodegeneration of retinal ganglion cells (RGCs), resulting in irreversible vision loss. Available therapies, which decrease the common causal risk factor of elevated intraocular pressure, delay, but cannot prevent, RGC death and blindness. Notably, it is changes in the anterior segment of the eye, particularly in the drainage of aqueous humor fluid, which are believed to bring about changes in pressure. Thus, it is primarily this region whose properties are manipulated in current and emerging therapies for glaucoma. Here, we focus on the challenges associated with developing treatments, review the available experimental methods to evaluate the therapeutic potential of new drugs, describe the development and evaluation of emerging Rho-kinase inhibitors and adenosine receptor ligands that offer the potential to improve aqueous humor outflow and protect RGCs simultaneously, and present new targets and approaches on the horizon.