Compositions, methods, and systems are provided for fluorescent polymerase enzyme substrates comprising protein shields for improving enzyme photostability in single molecule real time sequencing. Fluorescent polymerase enzyme substrates of the invention have a protein shield between the fluorescent dye moieties and nucleotide moieties of the polymerase enzyme substrate. The polymerase enzyme substrates have a nucleotide component and a dye component, each attached to a protein. The attachments can be covalent. The protein can, for example, prevent the direct interaction of the fluorescent dye moiety with the enzyme when carrying out nucleotide synthesis, preventing photodamage to the enzyme. The polymerase enzyme substrates of the invention can have multiple dyes and multiple nucleotide moieties.