RESEARCH ARTICLE Molecular Details of Olfactomedin Domains Provide Pathway to Structure-Function Studies

Olfactomedin (OLF) domains are found within extracellular, multidomain proteins in numer-ous tissues of multicellular organisms. Even though these proteins have been implicated in human disorders ranging from cancers to attention deficit disorder to glaucoma, little is known about their structure(s) and function(s). Here we biophysically, biochemically, and structurally characterize OLF domains from H. sapiens olfactomedin-1 (npoh-OLF, also called noelin, pancortin, OLFM1, and hOlfA), andM.musculus gliomedin (glio-OLF, also called collomin, collmin, and CRG-L2), and compare them with available structures of myo-cilin (myoc-OLF) recently reported by us and R. norvegicus glio-OLF andM.musculus latro-philin-3 (lat3-OLF) by others. Although the five-bladed β-propeller architecture remains unchanged, numerous physicochemical characteristics differ among these OLF domains. First, npoh-OLF and glio-OLF exhibit prominent, yet distinct, positive surface charges and copurify with polynucleotides. Second, whereas npoh-OLF and myoc-OLF exhibit thermal stabilities typical of human proteins near 55°C, and most myoc-OLF variants are destabi-lized and highly prone to aggregation, glio-OLF is nearly 20°C more stable and significantl