What does this concatenation of values accomplish for you? Depending on why you need this, the calculation field may not be needed at all.
That said, field 5 can be defined as a calculation field with Text selected as the result type:
Field 1 & Field 2 & Field 3 & field 4
I am attempting to create a naming system for protein conjugates, there are a huge variety of possible combinations and this was the best system I could come up with!
Thanks in advance for your help!