Nanostructural control of gallium oxide formation is achieved at low temperatures by the enzyme-catalyzed hydrolysis and polycondensation of gallium oxide precursors. Filaments of silicatein, a hydrolase originally discovered in a marine sponge, catalyze the hydrolysis of gallium(III) nitrate, producing oriented nanocrystallites along the length of the filaments (see Figure) in the absence of acid or alkali.