Check out this great paper on using peptides to guide gene delivery. Most in vivo gene delivery systems use viruses to deliver genetic cargo to a particular cell. A peptide delivery system would have to meet certain goals including protecting the DNA, targeting specific cell surface receptors, disrupting the endosomal membrane, and delivering the cargo DNA to the nucleus. This paper has a table listing several peptides that can meet these four goals. Here is a copy of figure 1 that outlines these conditions:
The paper goes into great detail about using peptides for gene delivery, specifically talking about receptor specificity, endosomal escape, and nuclear localization. I had never even heard of using a protcetive peptide for gen therapy.
Very cool. Give the article a read if you have the chance.