The secreted glycoprotein, sclerostin alters bone formation. To gain insights 
into the mechanism of action of sclerostin, we examined the interactions of 
sclerostin with bone proteins using a sclerostin affinity capture technique. 
Proteins from decalcified rat bone were captured on a sclerostin-maltose binding 
protein (MBP) amylose column, or on a MBP amylose column. The columns were 
extensively washed with low ionic strength buffer, and bound proteins were 
eluted with buffer containing 1M sodium chloride. Eluted proteins were separated 
by denaturing sodium-dodecyl sulfate gel electrophoresis and were identified by 
mass spectrometry. Several previously unidentified full-length 
sclerostin-interacting proteins such as alkaline phosphatase, carbonic 
anhydrase, gremlin-1, fetuin A, midkine, annexin A1 and A2, and collagen α1, 
which have established roles in bone formation or resorption processes, were 
bound to the sclerostin-MBP amylose resin but not to the MBP amylose resin. 
Other full-length sclerostin-interacting proteins such as casein kinase II and 
secreted frizzled related protein 4 that modulate Wnt signaling were identified. 
Several peptides derived from proteins such as Phex, asporin and follistatin 
that regulate bone metabolism also bound sclerostin. Sclerostin interacts with 
multiple proteins that alter bone formation and resorption and is likely to 
function by altering several biologically relevant pathways in bone.