title: Carboxy terminus of secreted phosphoprotein-24 kDa (spp24) is essential for full inhibition of BMP-2 activity.
abstract: Secreted phosphoprotein-24 kDa (spp24) is a bone morphogenetic protein (BMP)-binding protein isolated from bone. It exists in a number of size forms and is hypothesized to function as a BMP latency protein and/or a "slow release" mechanism for BMPs involved in bone turnover and repair. We have examined the hypothesis that proteolytic modification of the C-terminus of spp24 affects its BMP-2-binding properties and bioactivity in the BMP-2-stimulated ectopic bone forming bioassay. Three different size forms of recombinant spp24 that correspond to predicted 18.1 kDa, 16.0 kDa, and 14.5 kDa proteolytic products were compared to full-length (fl) spp24. One of these forms (spp18.1) we hypothesize to be the protein which Urist initially, but apparently inaccurately, called "BMP." Only full-length spp24 completely inhibited BMP-2-induced bone formation. The 18.1 kDa truncated isoform of spp24 which we hypothesize to be Urist's protein did not. The inhibitory capacity of the proteins was correlated with their kinetic constants, assessed by surface plasmon resonance. At the highest, inhibitory, dose of spp24 and its derivatives, k(d) ("stability") best predicted the extent of ectopic bone formation whereas at the lowest dose, which was not inhibitory, k(a) ("recognition") best predicted the extent of ectopic bone formation. We conclude that proteolytic processing of spp24 affects the interaction of this protein with BMP-2 and this affects the function of the protein.
authors.affiliation: Geriatric Research, Education, and Clinical Center (11-E), VA Medical Center, VA Greater Los Angeles Health Care System, 16111 Plummer Street, Sepulveda, California 91343, USA.
authors.forename: Elsa J
authors.initials: EJ
authors.lastname: Brochmann
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Simon
authors.forename: Janusz
authors.initials: J
authors.lastname: Jawien
authors.forename: Keyvan
authors.initials: K
authors.lastname: Behnam
authors.forename: Chananit
authors.initials: C
authors.lastname: Sintuu
authors.forename: Jeffrey C
authors.initials: JC
authors.lastname: Wang
authors.forename: Samuel S
authors.initials: SS
authors.lastname: Murray
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D055396:Bone Morphogenetic Protein 2 / Q000378:metabolism*; D001842:Bone and Bones / Q000166:cytology / Q000502:physiology*; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D010012:Osteogenesis / Q000502:physiology*; D010750:Phosphoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D040901:Proteomics; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020349:Surface Plasmon Resonance; D015503:Surgical Sponges
chemical_list: C525719:Bmp2 protein, mouse; D055396:Bone Morphogenetic Protein 2; D010750:Phosphoproteins; D011994:Recombinant Proteins; C091340:secreted phosphoprotein 24