OPT to Green card

I am on OPT expiring May 2019 and have an active job offer. My employer is willing to sponsor me for the GC process. What options do I have for me and my employer? can I file for I-485? (sorry if I am wrong, read about I-485 in other blogs)

No you cannot .

https://redbus2us.com/qa/13616/green-card-application-while-on-opt