Functional Tests for the Characterization of Surfactant Protein B (SP-B) and a Fluorescent SP-B Analog

Surfactant protein B (SP-B) enhances lipid insertion into the alveolar air/liquid interface upon inhalation. The aim of this study was (i) to apply a palette of tests for a detailed biochemical and biophysical characterization of SP-B and (ii) to use these tests to compare native SP-B with a fluorescent (Bodipy) SP-B analog. The method of labeling was fast and resulted in a covalent fluorophore–protein bond. The ability of both proteins to spread a surfactant film on top of a buffer surface was determined in a spreading tray using the Wilhelmy plate technique to allow detection of alterations in surface tension and calculation of spreading velocities. In a captive bubble surfactometer surface tensions of spread films were measured. Similar biophysical properties were found for both native and Bodipy-labeled SP-B. It is concluded that the combination of tests used allows detection of small differences in structure and activity between the two proteins.