(190e) Obtaining Protein Solvent Accessible Surface Area (SASA) When Structural Data Is Unavailable Using Osmotic Pressure

A major problem in analyzing protein complexes is the inability to know the protein solvent accessible surface area (SASA) when their structures are unavailable. Here we provide an algorithm, via the free‑solvent osmotic pressure model, that predicts SASA using only concentrated solution osmotic pressure data. Sheep hemoglobin monomer and bovine β-lactoglobulin are used to verify this method. In addition, the SASA for the structurally-unknown calf lens α‑crystallin aggregate is predicted. Using osmotic pressure data, the predicted SASA value for sheep hemoglobin, 22,398 ± 1,244 Å², was in excellent agreement with the computational model predictions from the x‑ray diffraction structure (24,304 Å²‑26,100 Å²). Similarly, the SASA values for bovine β‑lactoglobulin, determined from osmotic pressure data of pH solutions 5.1, 6.0, and 8.0, were 5,765 ± 1,031 Å², 6,656 ± 1,082 Å², and 9,141 ± 1,060 Å², respectively, were in good agreement with the computationally determined SASA value (7,500 Å²-8,628 Å²). In addition, the SASA for the aggregate of calf lens α‑crystallin (800 kDa) was found to be 417,691 ± 16,790 Å². These results illustrate that this novel method can provide an important experimental alternative in estimating SASA for proteins and, possibly, their complexes in solution.