Can DMPfold and I-Tasser work well for de novo structure prediction of 1135 amino acid long sequence? I am trying to perform de novo structure prediction of a 1135 long protein sequence; can DMPfold and I-Tasser work well for de novo structure prediction of 1135 amino acid long sequence?
For DMPfold you might like to look at Figure 5B of the paper, which implies that performance starts to drop off after ~600 residues. Only proteins up to 500 residues were used in the training set, for example.

A protein of that length is almost certainly multi-domain. I would consider doing domain prediction; we have a tool DomPred, but many others are available. Then run the sequences of the domains individually and recombine them later.

I don't know about I-Tasser's ability to do this, perhaps see if they mention it in their papers.