"Fast Talk" is a non-diatonic, blues based progression which we are all familiar hearing, but doesn't conform to strict major scale harmony. However, that doesn't mean the progression doesn't have a tonal center; it’s actually rooted at the A7 chord. The chords in this progression are A7 - C7 - D7 - G7 - G#7, forming a blues/R&B harmonic structure. If we analyze the progression using Roman numerals, it's I7 - bIII7 - IV7 - bVII7 - VII7. Try playing A minor pentatonic over this progression when soloing.