Peptide coatings can help nanoparticles slip into cells, a process that may prove useful for in vivo imaging or drug delivery if scientists can clear up how it works. Now, Abdulaziz Anas, Mitsuru Ishikawa, Vasudevanpillai Biju, and coworkers with Japan’s National Institute of Advanced Industrial Science & Technology have a better idea after thoroughly studying the insect neuropeptide allatostatin and learning that it helps CdSe-ZnS quantum dots pass through cell membranes by recruiting clathrin, a protein that facilitates endocytosis by forming vesicles around foreign substances (ACS Nano, DOI: 10.1021/nn900663r). The researchers suspected that allatostatin might be gaining access to cells via galanin receptors. But when they blocked those receptors, it didn’t have much influence on the influx of quantum dots. By inhibiting PI3K, a kinase that is crucial to the formation of clathrin vesicles, they noted that fewer than half of the quantum dots made their way in, leading the team to conclude that most of the nanoparticle entry is clathrin-mediated. The remainder of the quantum dots may be entering through electrostatic interactions with molecules in the cell membrane, thanks to an arginine residue on allatostatin, they suggest.