The Protagonist is one of the most misunderstood characters in a story's structure.  When creating your Protagonist, don't let him or her get bogged down with all kinds of additional dramatic jobs that may not be necessary for your particular story.

It is often assumed that this character is a typical "Hero" who is a good guy, the central character, and the Main Character.  In fact, the Protagonist does not have to be any of these things.  By definition, the Protagonist is the Prime Mover or Driver of the effort to achieve the goal.  Beyond that, he, she, or it might be a bad guy (such as an anti-hero).

Being the Central character just means that character is the most prominent to the audience.  For example, Fagin in "Oliver Twist" is perhaps the most prominent, but he is certainly not the Protagonist.  So, a Protagonist may actually be less interesting than the Antagonist, or may actually be almost a background character.

In addition, the Protagonist is not always the Main Character, who could be any one of the characters in your story who represents the reader or audience position in the story.

So, the only attribute you should consider in selecting your structural Protagonist is whether this character is the one with the most initiative toward reaching the Goal.