Yeast peptide goes forth and multiplies.

Even the most efficient corporation would envy the teamwork exhibited by the molecules in a cell. At some point, though, before the first cells appeared on Earth, organic molecules would have been on their own, replicating without help from others. So far, scientists studying the origin of life have come across RNA-like molecules that can perform this trick, but no one had proved that proteins could do the same - until now.

Researchers have found the first evidence that peptides, short chains of the amino acids that make up proteins, can copy themselves by aligning and joining two pieces. Since much of the effort to understand the origin of life has focused on RNA (SN: 11/26/94; 8/10/96, these results may broaden the thinking on self-replication in biological molecules, some scientists say. Whether the results will influence theories about the origin of life, however, must be determined by further studies. The ideas may also lead to new ways of synthesizing chemicals.

M. Reza Ghadiri and his colleagues at the Scripps Research Institute in La Jolla, Calif., demonstrated self-replication in a peptide. Made of 32 amino acids wound into a tight helical structure, the peptide came from a yeast protein that regulates the activity of genes in the cell. The scientists reported their results in the Aug. 8 Nature.

The researchers took two near-halves of this peptide, one segment with l5 amino acids and the other with 17, and allowed them to react in solution. They saw that the presence of completed peptides caused the segments to assemble at up to 500 times the expected rate.

The peptides catalyzed the reaction, acting as matchmakers. The segments lined up alongside the full molecule, coming close to each other in an orientation amenable to bonding. Otherwise, the segments would have been left to bump into each other at random while floating in the vast solution.

This yeast peptide does not play a special part in theories about the origin of life. "There's nothing magical about this particular sequence," Ghadiri says. "It's one of the most well-studied, so we know the molecular interactions of this peptide." Its simple helical structure and its ability to form a paired molecule made it a good candidate for acting as its own catalyst.

On the other hand, RNA has the important quality of being able to transmit information. That doesn't mean peptide cannot, says Leslie Orgel, a chemist at the Salk Institute for Biological Studies in La Jolla, but "right now, it appears that this peptide fits into the category of non-informational self-replication."

Unlike RNA, whose information resides in its nucleotide sequence, a peptide's three-dimensional structure must be considered before concluding that it does not transmit information, responds Ghadiri.

Stuart Kauffman, a theoretical biologist at the Santa Fe (N.M.) Institute, calls the results "very exciting." He finds in them support for his own theories about "collectively autocatalytic" systems, set containing molecules that act as catalysts for each other.

He cautions, however, that Ghadiri, finding "could be a quirk of a single peptide or of a class of peptides," something further experiments should determine.

Gerald F. Joyce, also a chemist a Scripps, agrees that the peptide's behavior is not "general-purpose, but maybe that's OK." If self-replication happens in large enough set of peptides, even though it's not universal, he says, it opens up the interesting possibility that a natural selection process occurs. That would suggest that peptides could evolve.

"There's no reason why there should not be many [other examples]," Ghadiri says. "I should go buy a lottery ticket if I were so lucky as to pick the only one."