The present invention relates to a chimeric protein that includes an N-terminus coupled to a C-terminus, where the N-terminus includes a portion of a paracrine fibroblast growth factor (“FGF”) and the C-terminus includes a C-terminal portion of an FGF23 molecule. The portion of the paracrine FGF is modified to decrease binding affinity for heparin and/or heparan sulfate compared to the portion without the modification. The present invention also relates to pharmaceutical compositions including chimeric proteins according to the present invention, methods for treating a subject suffering from a disorder, and methods of screening for compounds with enhanced binding affinity for the αKlotho-FGF receptor complex involving the use of chimeric proteins of the present invention.