Aplysia LAPS18-like protein (ApLLP)  -  DNA

Biological function
Aplysia nucleolar protein ApLLP is a transcriptional activator, which binds to the cAMP- response element (CRE) and thus induces ApC/EBP expression required for establishing long-term memory.

Structural evidence
All three ApLLP forms had the far-UV CD spectra typical of a highly unstructured protein lacking of any predominant secondary structure. ApLLP is capable of binding the CRE DNA element but this induces no significant change in its secondary and tertiary structures. No significant increase in the HSQC spectral dispersion was observed for ApLLP-87 in complex with DNA, indicating that the binding would not induce the formation of the tight tertiary packing. The far-UV CD spectrum only underwent very minor changes, indicating that the secondary structure changes of ApLLP-87 triggered by DNA-binding were very subtle.

Biochemical evidence
The DNA-binding residues are mainly located on the C-half of the ApLLP molecule, involving a lysine rich motif. This plays a critical role in interacting with the CRE DNA sequence.

Mechanism category
conformational selection

Fuzziness of ApLLP might enable dynamic regulation of synaptic facilitation in Aplysis neurons.