The wild type (WT) amyloid-beta (10-35) peptide, Abeta (10-35), and its F19T mutant have been studied by molecular dynamics simulations at 340 K in explicit water solvent each for over 3.4 ms. The WT peptide has a strong preference to form an E22-K28 loop (44% of total conformations) and a reasonable stability for a strand-loop-strand (SLS, L17-M35) (9%). The F19T mutant has a significantly lower population of E22-K28 loop (14%) and SLS structure (1.7%), but has a high population of Q15-D23 loop (48%). A specific interaction pattern among D23, V24, E22 and K28 was found to stabilize the E22-K28 loop in WT. Our results are in agreement with several experimental observations including: (1) the NOE constraints for the Abeta are reproduced; (2) the regions (15-23) and (22-28) can form loops; (3) the WT peptide is more structured than the F19T mutant. The current results also support our early proposal that the SLS structure might be important intermediate for monomer deposition to fibril, which explains the experimental fact that F19T mutant resists deposition to fibril.