Human Pin1, a member of the parvulin family of peptidyl-prolyl isomerases(PPIases), catalyzes the phosphorylation dependent prolyl-peptide bond isomerization of phosphoserine/phosphothreonine-proline(pS-P or pT-P) containing proteins. Pin1 contains a C-terminal peptidyl-prolyl cis-trans isomerase domain and an N-terminal WW domain. WW domains, characterized by two fully conserved tryptophans (hence the name WW) spaced 20-22 amino acids apart, are typically 35-40 amino acids long and exist as one of the smallest naturally occurring monomeric proteins without the addition of co-factors, ligands, or the formation of disulfide bonds. We have shown in our lab that the Pin1 WW domain binds to phosphorylated Tissue Factor Cytoplasmic Domain (TFCD). Here, we report the structure of 13C/15N labeled Pin1-WW domain in complex with phosphorylated TFCD. Backbone assignment of the domain was determined using HNCA, HNCACB, HN(CO)CA, CBCA(CO)NH, HNCO, HNCACO NMR spectra and side-chain proton assignment using HCCH-COSY, HCCH-TOCSY, and N-TOCSY spectra acquired by 800 and 600MHZ Bruker-Avance magnets at 285K. Isotope selective filter (13C/15N) NOESY experiments, which detect intra-molecularly interacting protons, were acquired for determination of distance constraints used in DYANA theoretical annealing calculations. Further structure refinement using DYANA and AMBER 8.0 is currently in process. Determination of the structure of Pin1-WW domain complexed with phosphorylated TFCD will shed light into how Pin1 may regulate the phosphorlyation/dephosphorylation of TFCD . This research is funded by NIH-PO1-HL016411-32 as well as the Rice-Houston Alliance for Graduate Education and the Professoriate(AGEP) program.