Asymmetric Helical refinement (sym or convergence problem)

Hello,

I have an asymmetric helical refinement job that gives resolution of 6.69 A.

As sometimes cryosparc doesn’t converge at the 1st attempt, I thought I should ve run again the job. So, I took the first output volume (flipped as helices usually are expected to be right handed) and I’ve used it as reference map to lunch a second (asymmetric) helical refinement job. As attached, the new job resolution didn’t improve much: 6.59 A. The GSFSC doesn’t seem to have spikes or artifacts.


Screenshot 2022-08-03 at 10.37.11 AM

I understand it’s an asymmetric refinement and I need to find the (still unknown) symmetry to reach high-res. However, I don’t understand how I can’t push more given that my Nyquist is 1.72 A and have nice 2D classes (1.5M particles total).

Do you have any thoughts on how to improve the resolution in order to make (reliable) biased symmetrical guesses from the real space? In alternative, do you have any recommendations before I try every symmetry solution (>60 symmetries)?

Cheers
Lorenzo